The ancient guzheng had 12 strings, which gradually evolved into the modern form. Tuned pentatonically over four octaves, it has existed since the Warring States Period and became especially popular during the Qin dynasty.
Until 1961, the common guzheng had 18 strings. In 1961 Xu Zhengao together with Wang Xunzhi introduced the first 21-string guzheng after two years of research and development. In 1961, they also invented the "S-shaped" left string rest, which was quickly adopted by all guzheng makers and is still used today, whether in the shape of the letter "S", "C", etc.
2.Guzheng (pronunciation) is also known as Qin Zheng because it originated from the Qin state (located in today's Shaanxi province) during the Spring and Autumn Period and Warring States Period (771 -221 BC). It is also commonly known as Guzheng (Gu standing for "ancient" in Chinese) because of its long history, similar to the Chinese seven-string instrument, which is called Gu Qin (Qin being a general name for certain musical instruments). After Guzheng was introduced to Korea, Japan and Vietnam, it was then known as Kayagum in Korea, Koto in Japan and Dan Tranh, with sixteen strings, in Vietnam. Over the years, these variations have developed with their own characteristics. In this sense, both Qin Zheng and Guzheng can be called Chinese Guzheng.

The early Guzheng instruments had 5 strings and gradually evolved with the number of strings increasing to 12 in the Han Dynasty, 13 in the Tang Dynasty, 14 and 15 in the Ming Dynasty, and in most recent times 16, 18, 21, 23 and 26 strings.

In its early history, Guzheng was mainly used in ensemble music and to accompany singing. The emergence of "xiang he ge" (song with harmony) in the Han Dynasty (206 BC - 220 AD) marked a whole new phase of development for Guzheng as a music art form.

With the development of "xiang he" musical genre, the Guzheng took on a more definite form by the 3rd century. It had oblong body of 6 Chinese feet long, with acurved soundbox on which 12 strings were stretched. It had high bridges, which gave it a high tonal range. In performing practices, the strings were plucked with plectra made of bone worn on the fingertips, thus producing crisp notes.

The art of Guzheng reached its height of development during this period. In the music of of the Estern Jin (317 - 420 AD) and the Northern and Southern Dynasties (420 - 581 AD), "qing shang yue" genre, which appeared after "xiang he ge", the Guzheng was widely used to perform ethnic songs in the region of today's Jiangsu, Zhejiang and Hubei provinces.

By the Sui Dynasty (581 - 618 AD), the 13-string Guzheng had already become an important instrument in court music, but the 12-string model continued to exist in the "qing shang yue", which evolved during the Sui and Tang Dunasties (cca. 7th to 10th century). It only started to decline by the end of the Tang Dynasty, and was replaced by the 13-string model. The turbulent and war-torn years of the Southern Song Dynasty (1127 - 1279) saw many music traditions disappearing.

The Guzheng continued to evolve during the Ming Dynasty (1368 - 1644), and the range grew broader with the number os strings increasing to 14 and 15. However, the social climate tended to disparage Guzheng music as one of plebeian taste, so it was spurned by the literati officials. Guzheng players also had a low social status. Since the skill and repertoire was taught orally, none of the ancient scores remained intact to present day.

During the Yuan and Ming Dynasties (cca. 13th to 17 century), operatic music and narrative singing became a major source of influence. During the 15th century, there was a popular music type in the northern part of China called "xian suo" (string music). It featured Guzheng, Pipa and Sanxian in ensemble playing or as accompaniment to singing.

From the early days when the Qin Guzheng was intruduced to the Central Plains, it had spread to other regions, covering what is today's Shaanxi, Henan, Hubei, Hunan, Jiangsu and Zhenjiang. Later, with 3 migrations of the Hakkas, the Qin Guzheng was introduced to Fujian and Guangdong. The art of Guzheng was thus spread to all parts of China. Everywhere it went, it was subject to the geography, climate, customs, dialect of the locale, and was assimilated into the folk music of the region. Different vernacular styles were eveolved, and in the 20th century, they became stylistic schools with their own provenance. The most famous Guzheng schools include Henan, Shandong, Chiuchow, Hakka, Zhejiang etc., all of which have a long history that dates back to at least the Qing Dynasty.