The paper studied the debris flow gully of hydropower station dam area in the upperstream of Yellow river based on the method of extension grey relational analysis. By applying the method of extension theory, the matter-element model of hazard evaluation for debris flow gully was established. According to the weighted value of evaluation factors in method of grey relational analysis,it then set up analysis model and analyzed the hazard of debris flow gully.Comparing with the method of fuzzy mathematics and standard,the,the results are vary similar and coincides with field investigation,. The conclution showes that the method is well applicabile in assessment of debris flow risk, and solved the diversity,complexity and uncertainty of debris flow.