Abstract: Diurnal changes of photosynthesis and light response curve of Pinus kesiya Royle ex Gordon var.langbianensis were measured with L icor26400 in dry season, and the relationship among the photosyntheticphysiological factors and the ecological factors were analyzed. The results showed that the net photosynthetic rate(Pn), transp iration rate ( Tr) andWater Use Efficiency (WUE) of P. kesiya Royle ex Gordon var. langbianensishad a diurnal change with three peaks respectively in dry season, the peaks of Pn occurred at 12: 00, 14: 00 and 17:00 respectively when the light intensity and temperature reached the highest level (14: 00), while intercellular CO2concentration (Ci) changed in an adverse way. The correlations between Pn and PAR, Ta, RH, Tr and PAR, Ta,RH, Cond and PAR, Ta, RH fitted quadratic curve model respectively. There was a significant positive correlationbetween Pn and photosynthetic active radiation ( PAR ) ( P -2 · s-1 showed as typ ical heliophyte, and it belongs to the high light energy potentialp roductivity tree for its photosynthetic characteristics of high photosynthetic efficiency.