Abstract: Mr.Zhang Ruzhou systematically sorted out the whole developing process from the theory of observing celestial phenomena and setting astral time to the Quarter Calendar.He established a concise and practical view of the ephemeris,restored the algorithm of the Quarter Calendar,and pioneered the systematic method of "Three Evidences Consistent in One" in historical research.His theory has solved many difficult problems in the astronomical calendars before the Han Dynasty,and was successfully applied in the study of the annals of the Western Zhou Dynasty,and achieved fruitful results.The entire theory has been established for more than sixty years,and it is still unique in studies of the history of astronomy that is booming today.This article presents in detail Mr.Ruzhou's enormous contribution to the study of ancient astronomical calendar and ancient history chronology in five aspects.In particular, Mr.Zhang Ruzhou clarified the mists of "Jupiter Calendar" and the statement on the "Three First Months" of the Xia, Shang and Zhou Dynasties.He clarified that "Zhong, Liu, Fu and Na" are used under the ancient method for quantitatively describing the star position.He translated,compared and interpreted several important ancient books on observing celestial phenomena and setting the astral time.He revealed the truth of the "Three-General Calendar".He invented the modified algorithm of Quarter Calendar.