A site of building is located in the Dagou drainage area,the upper reaches of Minjiang river,where the debris flow and flush flood often occur.The risk of the site bringing by,possibly,the debris flow and flush flood is analyzed from the aspects of the characteristics of the debris flow,flush flood and its embranchments,the scale of its breaking out,and the influence of flush flood character in the ravine brought by the debris flow of its embranchment.Then the site was divided into several sections by risk extent of the debris flow of its embranchment.The results show that the main body of the site lies in the no2hazard area,so the plan is feasible.