[Objective] The objective of this study is to analyze the impact of debris flow on the main river and the possibility of debris flow blocking the main river.[Methods] We conducted experiments for the debris flow blocked river tests, and analyzed the debris flow blocking the river cases in history.[Results] Three basic modes of debris flow blocking river were concluded according to debris flow motion and deposition morphology. These modes included top damming block mode, seepage mixed jamming burst mode and narrow beam progressive blocking mode. Based on three modes, we studied the motion and the disaster mechanism of the debris flow blocking river.[Conclusion] The top rushed damming block mode was characterized as the top leading rushed across the side bank, provenance stuffed the main channel and the fragile parts seeped to the collapsed body. The seepage mixed jamming burst mode was characterized as short-term crammed into the main channel, water permeability mixed jam and increased flow. The narrow beam progressive blockage model was characterized as based groove section of narrow beam, local flow transient increasing and gradual local blockage. The current history in the river blocking events is mainly narrow and progressive blockage, and the results agree with the experimental results.