The formative environment of debris flow is analysed by means of investigation in Fangduigully of Wenshui county.It is considered that Fangduigully is a typical complex debris flow gully affected by human actions.There is no clear distinction between areas of solid materials accumulation and passage way.At last,the debris flow of Fang duigully is predicted.The conclusion is that if there is no control engineering,the debris flow will become more serious when storm occurs.