Density is the most fundamental parameter to describe the physical property of debris flow.It is of great significance for evaluation and mitigation of debris flow. Methods: Based on the temporal and spatial characteristics of hydrology process,considered the physical connotation of density,this paper described three characteristic values of debris flow density: max-density,peak-density,and mean-density.By used the debris flow observation data in Jiangjia gully since 1987,the distribution law and influencing factors of density are also analyzed Results: The result shows that those three characteristic density values can be used to express the temporal and spatial evolution of debris flow process.The peak-density and mean-density both can be calculated by max-density.The density value is impacted by the peak discharge of debris flow,but not the Volume.A new method of density calculation,which contains the sampling of debris flow deposit,formula calculation, verification,and the principle of using,are established for debris flow mitigation.The max-density can be recommended for the calculation of peak discharge, velocity,and impact pressure,while the mean-density can be recommended for the calculation of the total volume of soil materials,the danger of river blocking,and the scope of dangerous areas.