Studying the trend of crop water demand and identifying key influencing factors can provide a basis for scientific crop irrigation, improvement of agricultural water use efficiency, and optimal allocation of water resources. Based on the daily meteorological data of Jiansanjiang Reclamation Area from 1995 to 2018, according to the Penman-Monteith formula combined with the single-crop coefficient method, the water requirement of the main crops of rice, corn, and soybeans during the growth period were calculated. Using the trend-free pre-whitening Mann-Kendall (TFPW-MK) method to study the change characteristics of the water demand of three crops, adopt the rescaled range (R/S) analysis method to predict the change trend of the future water demand of the crops, and the path analysis method was used to quantitatively analyze the influence of six meteorological factors such as average temperature, net radiation, sunshine hours, wind speed, precipitation, and relative humidity on crop water demand. The key influencing factors of water demand changes were determined, and the relationship between the change trend of key influencing factors and the change trend of water demand was analyzed. The results showed that the average multi-year water requirement of the reference crops in Jiansanjiang Reclamation Area was 606.68mm. The inter-annual changes in the water requirement of major crops such as rice, corn and soybeans during the growth period were relatively stable. There was a significant difference between the amount of water. The average multi-year water requirement of the three crops were 484.84mm, 425.91mm and 319.11mm, respectively. In the time series from 1995 to 2018, the water demand of rice and soybeans during the whole growth period showed an upward trend, while the water demand of maize during the whole growth period showed a downward trend. In the future, water demand during the whole growth period of rice and soybeans would increase, and water demand during the whole growth period of corn would decrease. Average temperature, radiation and sunshine hours were the key influencing factors for the water demand of rice, corn and soybeans, and they played a role in increasing the water demand. Precipitation increased the water demand of crops, but it was not obvious. Wind speed and relative humidity played a certain restrictive effect on the water demand of the three crops. Therefore, the water demand of rice, corn and soybeans in Jiansanjiang Reclamation Area was affected by many influencing factors. The change trend of water demand caused by the changes of meteorological factors during the whole growth period of rice and soybean was consistent with the change trend of water demand of rice and soybean in the TFPW-MK test analysis. The increase in the average temperature during the whole growth period of corn was not enough to offset the influence of radiation and the reduction of sunshine hours on the water requirement of corn, so the water requirement of corn showed a downward trend, which was consistent with the change trend of water requirement of corn in the TFPW-MK test analysis.