Abstract: Global climate warming is an indisputable objective fact, and it inevitably impacts agricultural water use and grain security production in China. In this paper, the Palmer drought severity index (PDSI), the gross irrigation quota (GIQ) and the per-hectare grain output (PHGO) were used as specific indexes of climate change, agricultural water use and grain production to analyze inter-annual variation characteristics and correlation between PDSI, GIQ, PHGO in China from 1949 to 2005, and a good linear correlation between PHGO during 1949-1983 and PDSI as well as GIQ during 1949-1990 was found, which indicated that climate change significantly affected agricultural water use and grain production, while human factors (technological progress, policies mechanisms, production inputs, etc.) affected relatively small at above-mentioned stage. According to the correlation, the GIQ and PHGO during 1949-2005 were predicted. It was found that predicted values and actual ones of the GIQ during 1949-1990 and the PHGO during 1949-1983 had poor relationships, which indicated that human factors (technological progress, policies mechanisms, production inputs, etc.) gradually became the leading position, and their average impact rate on agricultural water-saving and grain yield reached over 27% and 40%, respectively. The negative impact of climate change on agricultural water use and grain production can be mitigated to some extent by controlling the human factors as technological innovation, policy mechanisms protection as well as production inputs increment.