Abstract: Grain production is affected by many factors .The paper analysed the impact on grain production by the factors which are natural and economic and social firstly .The paper studied the output of per area and area scale comparative advantage and integration comparative advantage of main grain crop from 1979 to 2003 in the three main grain production areas which are Changjiang mid-catchment area and Huang huaihai area and Dongbei area and Summed up the integration comparative advantage of the five main grain crop in the three areas .It proposed the ideas and countermeasures to bring into play comparative advantage of grain production and enhance grain integration production capability in the end.