Xinanjiang model is is widely used in humid regions and sub humid regions .The parameter of Xinanjiang model has a great influence on its simulation results. What’s more, there are many factors that affect the parameter of Xinanjiang model. Among them, whatever in different or in the same basins, the area of small watershed has certain effect with the parameter of Xinanjiang model. In this paper, the research is based on Yandu River, in which Yandu River basin is respectively divided into different small watershed. There are three different ways of divisions to make the number and the areas of units changed, and in each division the area of the units were similar. Respectively for three kinds of units division under the way of the field to simulate the flood adjustable parameter, finally got three groups of optimal parameters on average. Analysis of the three group of optimal parameters change, the size of the average can be concluded that the more the number of cell division, cell size is smaller, the Xinanjiang model parameters of CS, CI, CG.