Under the condition of lack of magnesium,effects of magnesium application on the sugar,starch,protein and fruit quality of grape were studied,in order to provide reference basis for formulating fertilization of grape.A field experiment with split plot design was conducted,in the main area four soil applied gradient of 0,112.5,150,187.5 kg/hm2were set up,in the deputy district three concentrations of foliar spraying of 0%,0.2%,0.4%were applied.The results showed that soil and foliar spraying magnesium fertilizer significantly improved the magnesium content in leaf,increased nitrate reductase activity,soluble protein and soluble sugar content,promoted the starch transhipment,reduced its accumulation in leaf,eventually increased the skin pigment content,made the skin become red,improved fruit total soluble solid content,reduced the content of titrable acid and improved the quality of the fruit from both external and internal.When soil appiled 150 kg/hm2 magnesium and foliar spraying 0.4%magnesium fertilizer,the content of magnesium in leaves was in the moderate amount,with high activity of nitrate reductase,high content of soluble protein and sugar,red fruit peel,low fruit sugar,and the effect of magnesium was the best.