Under the condition of lack of magnesium,effects of magnesium application on the photosynthetic rate and chlorophyll fluorescence of grape were studied in order to provide reference basis for formulating rational fertilization technique of grape.A field experiment with a split plot design was conducted,four soil gradient of 0，112.5，150，187.5 kg/ hm2 was set up in the main area,three concentrations of foliar spraying,which was 0%,0.2%,0.4%,respectively,was set up in the deputy district.The results showed that soil application and foliar spraying of magnesium fertilizer significantly improved the magnesium content in leaf,when soil application with 150 kg/hm2 and foliar spraying of 0.4%magnesium fertilizer,the leaf chlorophyll content,net photosynthetic rate,Yield,ETR,Fv/Fm,qP,qN are maintained at a higher level,but F0 was at the lowest level.A moderate amount of magnesium supplement significantly increased magnesium and chlorophyll content in the leaves,increased the net photosynthetic rate,increased nonphotochemical dissipation of PSⅡ antenna pigment,relieved damage optical system,at the same time,maintained PSⅡ in situ light energy conversion efficiency and potential activity,but when too much magnesium was applied,stomatal conductance decreased,which resulted in a decline of net photosynthetic rate.