Abstract: Effects of different light intensities and phosphate levels on photoinhibition of photosynthesis in satsuma mandarin(Citrus unshiu Marc.) leaves were studied in the culture solution. The results showed that under high light intensity and the condition of phosphate deficiency, initial fluorescence(Fo), maximal fluorescence(Fm), photochemical efficiency of PSII(Fv/Fm)and apparent electron transport rate (ETR) decrease, on the other hand, slow -phase (qNs) of non-photochemical quenching and leaf temperature increase. After treated by DTT, Fo was much higher than control(H2O). These results indicated that phosphorus deficiency stress aggravate photoinhibition of photosynthesis, xanthophyll cycle-dependent non-radiate energy heat dissipation played an important protective role against photo-damage to the photosynthetic apparatus in satsuma mandarin leaves during phosphate deficiency stress.