Although scarcity of irrigation water restricts grain production, it can promote agricultural technology progress to increase supply elasticities of grain. To shed light on the comprehensive effect of irrigation water pressure on grain production structure, this paper explores the effects of irrigation water pressure, grain price changes and their interaction on the yields of different crops based on heterogeneous coefficient Nerlove model and panel data of 27 provinces from 2002 to 2017. The results show that: (1) The direct effect of irrigation water pressure on grain production structure is increasing proportion of corn yield and reducing proportions of other crops yields. Specifically, the magnitude of that impact is in a descending order from rice, potatoes, beans and wheat. (2) The indirect effect of irrigation water pressure on grain production structure is decreasing supply elasticities of wheat, beans and potatoes while making supply elasticities of rice and maize even larger, which contributes to the increase of proportions of rice yield and corn yield. (3) With growth of irrigation water pressure from 2002 to 2017, its comprehensive effect on grain production structure makes a significant increase in proportion of corn yield and a significant decrease in proportions of beans yield and potatoes yield. Regional analysis reveals an increase in yield proportions of maize and rice in main grain production areas of Northern China, leading to more irrigation water consumption in this region where scarcity of water is severer. And this finding of our paper is a support for "the paradox of irrigation efficiency".