Photosynthetically Active Radiation(PAR) is an important energy source of photosynthesis for the green plants.In this paper,characteristics of the photosynthetically active radiation over Zhangye region are analysed and studied by using the data of solar spectral radiation during HEIFE FOP and BOP at Linze and Zhangye station,respectively.The results show:in clear case the ratio of PAR to global radiation is a range from 0.419 to 0.426 over Zhangye region and the seasonal variation is not obvious.In cloudy case,the ratio of PAR to global radiation is larger than that in the clear case,their seasonal variation is obvious,and the ratio is large in summer and small in winter.In addition,the empirical formula to calculate the PAR over Zhangye region is fitted base on the observed data and the distribution of PAR over Zhangye region is also discussed in this paper.