Abstract: In this paper, we build up the statistic relationship between the bulk density of debris flow slurry and integrity coefficient of watershed morphology by carrying out field investigation of 20 debris flow basins at the mountain areas of Sichuan province. With fitting analysis results, we fit the trend line and obtain the exponential formula to calculate the bulk density of the debris flow slurry, verifying the rationality of fitting formula by error analysis, effect factors analysis and tendency analysis. Primary research results show that integrity coefficient of basin shape exert a remarkable influence on the bulk density, which decreases when the integrity coefficient increases. The diluted debris flow or even water-stone flow is formed when the integrity coefficient is over 0.3, and the minimal value of bulk density is 1.28 t/m3 from calculation, which is very close to the current observed value. This method is especially suitable for those debris flows whose integrity coefficient of watershed morphology is relatively large. It can provide an easy way to calculate the bulk density of the debris flow which cannot be observed directly, and it is also helpful to determine the bulk density legitimately in some regions.