Cercidiphyllum japonicum Sieb. et Zucc. was listed as one of national protected plants at second category in Chinese Plant Red Book because of its population in extremely low quantity and small size. In the four selected populations from the geographic distribution areas occupied by the species of Houhe, Hubei; Hupingshan, Hunan; Mulinzi, Hubei and Laoshan, Anhui, each individual tree of C. japonicum was surveyed to get the data such as height and diameter at breast height. The age structure of every population was clarified by height class and diameter class instead of age class, and then the point maps were drawn based on the orientation data obtained from location instruments. Finally, the point pattern analysis was performed using Programita software. The results showed that the age structure of Houhe population presented the type of obviously uninterrupted spindle, which has meant a tendency of the population toward declining, whereas the other three populations didn't show uninterrupted age structures, indicating that they had declined. The Houhe population has the spatial distribution pattern of randomly distributing at scales ＜16m, but of clumped at scales ＞16m, while the other three populations tended to be randomly distributed at most of scales ＜100m. The analysis demonstrated that heterogeneous habitat in Houhe population might possibly result in formation of clumped distribution at bigger scales, while the similar environment and random seed dispersal could be responsible for random distribution at smaller scales. The reasons for decline and random distribution of the other three populations was due mainly to rigorous germination condition the species requires, few gap appearance, interspecific competition, habitat deterioration and so on. Some suggestions were also made for conservation of the species C. japonicum.