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An analysis is made of yield components, correlation between 30year yield per unit and meteorological factors in summer (May to September) in Heilongjiang Province by means of 50year grain production data of Heilongjiang Province. The results show that the fluctuation of the total grain yield is attributed to the fluctuation of average total grain yield per unit and the structural adjustment of planting structure. Since 1949, the proportions of corn and soybean yields to total grain yield have been almost kept unchanged, and the rice yield has been increasing year by year. The spring wheat yield presented a gradually increasing trend from 1949 to 1990, but sharply decreased since 1991. The yield per unit of rice was the highest, that of corn the second, spring wheat the third, and soybean the lowest. Comparison of grain yield per unit shows that there was a gradually increasing trend for various crops. The sunshine and temperature were major meteorological factors that influence grain yields in Heilongjiang Province.