Abstract: In March of 2015, 10 young Rhododendron simiarum trees were transplanted as potted culture from Songyang(altitude: 1 000 m) of Zhejiang province to Zhejiang Academy of Forestry (altitude: 24 m). In May of 2016, treatments of 10% of illumination and full exposure were carried out on 5 trees each. In July of 2016, determinations were implemented on their photosynthetic properties by LI-6400. The results showed that net photosynthetic rate(Pn) of R. simiarum trees under 10% illumination was higher than that under full exposure, indicating more adaptive to low light intensity at low altitude in the summer. Transpiration rate(Tr) of trees under 10% illumination was lower than that under full exposure, but water use efficency(WUE) was the opposite. R. simiarum under 10% light had more accumulation of dry matter. The diurnal variation of Pn, Tr and Gs was single-peak curve, but Ls and Ci had double-peak curve.