In order to evaluate quantitatively the effects of climate warming on grain filling of winter wheat,the field heating treatments and growth observation experiment on winter wheat were carried out.In light of the historic data,the statistical method was used to analyze the effects of warming on filling process of winter wheat,and to determine the heat damage index of winter wheat during grain-filling period in North China.The result indicated that the high temperature above 30 ℃ had significant inhibiting effect on grain filling of winter wheat.The length and intensity of high temperature(t≥30 ℃)per day jointly influenced the grain-filling rate,especially for the length of high temperature.The heat damage index during grain filling period of winter wheat was defined based on the length of high temperature in North China.When the days of high temperature(≥30 ℃ over 5 h per day)reached to 10 days and the high temperature process(high temperature lasting for 3 days)got once,it was defined as the mild heat damage.When the days of high temperature(≥30 ℃ over 5 h per day)reached to 11 days and the high temperature process(high temperature lasting for 3 days)occurred twice, it was defined as the moderate heat damage.When the days of high temperature(≥30 ℃ over 5 h per day)exceeded 11 days and the high temperature process(high temperature lasting for 3 days)appeared more than twice,it was defined as the severe heat damage.