Planetary theory is one of the core contents of traditional Chinese mathematical astronomy. There is a relatively complete planetary algorithm in the Triple Concordance System, the first system which is well preserved in China, and related content is found in all subsequent systems. Since predicting the positions of the five planets was one of the criteria for judging whether a system was effective, the planetary theory was constantly improved. The Great Expansion System occupies a very important position in the development history of Chinese planetary theory because of its many innovations. This paper comprehensively explains the planetary algorithm in the Great Expansion System, simulates the planetary algorithm in the Great Expansion System using the computer program Python, discusses the accuracy of the calculations of planetary positions in the 35 years when the Great Expansion System was used, and concludes that the maximum error of the longitude of Jupiter, Mars, Saturn, Venus and Mercury calculated by the system is as follows: 3.93°, 36.96°, 7.99°, 18.52°, 32.5°. Further analysis shows that the main factors affecting the error of the calculation of the planets in the Great Expansion System are as follows: the planetary Argument of Aspectual and Interval Count (the table of planetary equations of the center), the precision of planetary perihelion longitude, the date of conjunction of the planet with the sun and the constant of the planetary synodic period.
Lv et al. (Fri,) studied this question.