In the Manasi River Basin on the northern slope of the Tianshan Mountains, long-term and large-scale exploitation of groundwater has caused a series of ecological and environmental problems, and the water balance of groundwater and the flow pattern of groundwater have been changed obviously. In order to study the flow pattern of groundwater system under the condition of water saving irrigation and the change law of water saving irrigation to groundwater balance element,the dynamic changes of groundwater level and water balance in the Manasi River Basin were studied by using three -dimensional groundwater numerical simulation method and taking the plain oasis area as the research object. The results show that the uplift and fall of the groundwater level in the study area is significantly influenced by the agricultural irrigation, and has a certain periodicity, there are obvious differences in time and space. The balance of groundwater is negative, with a recharge and discharge difference of -2.81× 108 m3 . The correlation coefficient between the observed head and the calculated head for the simulation period is greater than 0.81, indicating the simulation effect is well.