The impact of climate change on grain production has become one of the hotspots in the research on global change.The impact of past climate change on crop yield is an effective approach for this research,however,it is difficult to separate the contribution of climate changes and human activities in such studies.Traditionally,the real yield is separated into trend yield that fits the real crop yield by a trend line depended on time only,and the fluctuant yield which is the residual yield between the real yield and the trend.The fluctuant yield is regarded as the climatic yield.But the main disadvantage of the traditional method is that it could not show the actual contribution of trend of climate change to yield of grain.In this paper a new method is put forward to calculate climate yield,which may overcome the disadvantage of traditional method. Climate influence coefficient that is the ratio of climate yield to trend yield is given to express the influence on the yield by meteorological factors.In the new method,a referenced period that satisfies the hypothesis of traditional method is selected to construct a function on the main meteorological factor and climate influence coefficient by regression.This function can be used to calculate climate yields beyond the referenced period.As a case,this method is used to calculate the climate yield of rice in Heilongjiang Province.Traditional methods,such as exponential function,polynomial function and moving average,are used to fit the per-unit-area rice yield for comparison.The comparative result shows that the contribution by climate warming can be revealed more accurately by using the new method.