|In the article, the water balance theorem was used for evaluating the consumptive characteristic of irrigation water on paddy fields, which in the condition of crop irrigated during the long-term period. The irrigation area of Huludum main canal was selected as an research region, and the each water records and hydrologic data in 2001-2005 was used to analyze. The results show that water requirement (WR) of paddy fields in the first and second crop periods were 1,593 and 1,381 (mm/crop period•ha) respectively. With considering the conveyance loss, the irrigation water requirement was intake from rivers were raised to 2,570 and 2,227 (mm/crop period•ha) in the first and second crop periods.The 5 years average of effective rainfall was conducted to analyzed as 293 and 242 mm in the first and second crop periods, and the usage ratio were respectively showed as 63% and 41%. The result revel the significance that effective rainfall played a subsidiary for irrigation in the first crop period. The study used the water balance theorem was conducted to analyze evaluate the consumptive characteristic of irrigation water in a large scale paddy region, and the results show the main consumption of water is to recharge the groundwater in paddy field system, and the the ratio was 48.80%. Return flow, evapotranspiration and effective rainfall were the subsequent in order, and the contributions were respectively showed as 20.45%, 19.92%, and 10.83%. Return flow was consists of visible return flow and invisible return flow, and the ratio between them in the first crop period and second crop period were respectively 1.85:1, and 3.13:1.