In early summer and autumn we studied the microclimate effect of mixed forest of P. orientalis and P. davidiana P. orientalis monoplantation as a contrast. The results showed: In early summer,the effect of air temperature decreasing around noon period was not clear,whereas in autumn the effect of air temperature decreasing around noon period increased along with density increase. The shading effect of P. davidiana increased moist degree and virtually increased precipitation by 26. 5mm during the growing season. Soil temperatures at 10 cm depth continually increased in the daytime. The times of rapid soil temperature increasing within P. orientalis and P. davidiana mixed forest were 0. 5 ~ 1. 0 h earlier than that of the P. orientalis monoplantation regardless of in early summer or autumn. And the maximum soil temperature increasing rate was lower than the P. orientalis monoplantation. In early summer,the phase of air humidity was reverse to that of air temperature,which was a typical characteristic of continental climate. In autumn,the typical characteristic of continental climate disappeared. The air humidity changed little. The averages of air humidity of different treatments were close to each other in early summer,whereas in autumn it increased along with forest density increasing. At noon period,when air temperature was high,shading helped photosynthesis. The paper concluded: P. orientalis and P. davidiana mixed forest reduced air evaporation capacity,decreased soil temperature rising rate and range,increased air humidity and gentled its fluctuation it was advantageous to reduce exceeding water consumption.