Abstract: With the method of sample survey,studies were made of the structure characteristics of the tree layer of plant communities on the sunny slope in Chuxiong Xishan Park. The results showed that the main arbor species were Pinus yunnanensis,Quercus acutissima Carruth,Castanopsis orthacantha,Pinus armandi,Keteleeria evelyniana and so on. The dominant families in low mountain zones were Fagaceae and Quercus. The dominant families in high mountain areas were Pinaceae and Pinus. With the increase of elevation,Shannon-Wiener index and Simpson index declined slowly, Margalef presented a single-peak distribution pattern,and Pielou index showed a bimodal distribution pattern. Arbor density first increased and then decreased with the enhancing of elevation. The DBH of trees were concentrated on Ⅱ、Ⅲ、Ⅳ diameter classes,such trees were mostly distributed in the middle and low altitudes.