The catastrophic debris flow disaster occurred in Zhouqu County in August 8, 2010 caused greatcasualty and property damage. Survey, empirical analysis and inductive inference were made to investigatethe causes of the Zhouqu debris flow disaster by analyzing the geological conditions of the debris flow. Two main causes were the natural factors like mountain collapse by earthquake, strong rainstorm suddenly oc-curred in a particular place and antecedent severe drought, and the human factors like disordered exploita-tion, poor flood control engineering quality and unreasonable urban development planning.Thus, the deep causes were derived, i.e.,the lacks of the environmental evaluation, early warning system and mechanisms for disasters, and consciousness for preventing and reducing disasters.The measures for prevention are put forward, i.e.,early warning, accurate monitoring and rescuing emergency. The establishment of the com-prehensive system of early warning and prevention may fundamentally prevent the recurrence of similar geo-logic hazards.