Abstract: Image grid cell is a widely used mapping unit type in GIS-based geohazard assessment. Values of each controlling factor should be calculated and endowed to grids. Risk levels can be determined through overlay analysis. However, due to the lack of quantitative computational model, the determination of grid size is largely dependent on expert experience. Taking Enshi City as an example, this paper analyzes the influence mechanism of grid sizes on the most commonly used controlling factors. The results can provide scientific basis for the determination of grid size.