The main research achievements in the area of risk assessment, hazardous dimension, and catastrophic prediction of debris flow are reviewed and summarized. The environmental geological condition of tailings debris flow in west ditch is introduced by the method of field survey and local observation. By taking use of the experiment model established based on 31 sets of debris flow experiment data, the hazardous dimension of debris flow is predicted, and the maximum accumulation length and area in West Ditch is obtained, comparing with the results of field investigation, it could be concluded that the experiment model method is more suitable for predicting the hazardous dimension of tailings debris flow. The gray system forecast model is used to predict the recently disaster time sequence, the credibility is good enough as contrasted with the monitor result, it is able to provide a reference for the risk assessment and disaster mitigation of debris flow. It is also able to provide new ideas for the disaster prevention and mitigation assessment caused by tailings debris flow.