Datong Tongzhan is a divination book compiled by the Imperial Board of Astronomy in early Ming dynasty, which preserves some positional data of stars observed at that time. Based on this star catalogue, a further research is carried out on star observation in early Ming dynasty. Firstly, through a deep analysis, it is found that this book should be completed between the 4th and 23rd year of Yongle reign. Then, with Hipparcos star catalogue (2007) as standard, Fourier analysis of the declinational error of these stellar data is carried out, which suggests that these data should be observed in Hongwu reign, and reach the highest level of accuracy before the end of Ming Dynasty. Besides, an investigation of the condition of the Imperial Board of Astronomy in early Ming dynasty demonstrates that the improvement of accuracy was mainly due to the betterment made by Guo Shoujing on observational instruments. Finally, the study on this accurate star catalogue further reveals historical changes of the ancient Chinese constellations.