Groundwater level fluctuations can be affected by a variety of human activities such as, designing the drainage and irrigation of farmland mining and utilizing water resources rationally, mine drainage, reservoir leakage, reservoir backwater and so on. Therefore, it is very important to study the dynamic variation of groundwater in arid areas for improving groundwater resources management strategy. We analyzed the groundwater level data of about 30 years for the Geermu alluvial fan. The paper describes briefly the character of the groundwater level changes and the influencing factors in different parts of the alluvial fan and divides the genetic types of groundwater system. Some characters are derived in natural conditions. Because of the low precipitation condition, the amount of precipitation doesn't affect the dynamic variation of groundwater in the area. The river flowrate (representing the infiltration capacity of river) is the most important factor of causing the fluctuations of groundwater level. However, in the plain areas, the influencing of river diminishes, and the evaporation is the first factor of causing the fluctuations of groundwater level.