Irrigation infrastructure construction is of great significance to improve agricultural production conditions and enhance agricultural productivity.This paper recalculates the total factor productivity of the crop industry in 27 provinces and autonomous regions of China from 1980 to 2018 based on agricultural input-output data and empirically analyzes the different effects of irrigation infrastructure on the total factor productivity of the crop industry in different periods using structural break model.The results show that although irrigation infrastructure has played an important role in promoting the total factor productivity of the crop industry in the past 40 years，its marginal impact varies significantly across regions and gradually decreases with the transformation and development of agriculture and rural areas，which leads to a trend of decreasing marginal rate of return on irrigation infrastructure investment over time. Based on these results，it is advisable to improve the efficiency of irrigation infrastructure through enhancing the regional layout of irrigation infrastructure investment and optimizing the direction of public investment .