In this paper,according to the situations of the express highway project(from Nanchang to Fengxin),the evaluation method of flood control influence by the engineering project inside channel was investigated.Through comparing the variation of design flood level and flood discharge before and after the engineering construction,the flood control influence by the engineering project was evaluated.It provides some evidence for the constructions of the express highway project(from Nanchang to Fengxin),It can provide a reference for this province and other areas to carry out a comprehensive flood prevention assessment of river related buildings.