Shoushi Calendar，the most outstanding calendar in ancient China，was compiled by Guo Shoujing，a prominent scientist in the Yuan Dynasty，and his colleagues. Enforced in 1281,throughout the Ming Dynasty and the begin-nin4 of the Qinq Dynasty，the calendar was used for over 360 years.

The reason why the calendar was used for such a long time has much to do with its accuracy in calculation. In the first place，it employed astronomical docu-ments of the highest accuracy in its time. For instance，it set the tropical year at 365.2425 days，which was the exactly the same as that in the currently used Gre-gorian Calendar, 301 years preceding the latter though. Secondly, based on earlier scholars finding that the length of the tropical year was gradually shortening，the Shoushi Calendar held that the tropical year shortened by 0. 0001 day every 100 years，which was more accurate as compared with earlier researches.

In addition，instead of the mathematical method of recording astronomical documents via complicated fractions，the calendar employed decimal fractions，which largely reduced calculation workload and guaranteed accuracy. It also made innovations in terms of calculation methods;for instance，the use of mathematical approaches like cubic interpolation，polynomial equations to the 4th order and spherical trigonometry.

Soon after its compilation，the Shoushi Calendar was Spread to and adopted by Japan and Korea. In recent years，astronomers from Japan，European and North American countries are again showing interests in ahe Shoushi Calendar，and some broad and in-depth researches have been made. As an advanced and accurate calendar in the history of China，the Shoushi Calendar also occupies a distinct posi-tion in the history of world astronomy.