The volume of dredging works of the Jiaokou Reservoir on Shichuan River in Shaanxi is very large, whether the sedimentation calculation will occur in the reservoir area or not after its impoundment is the key to success of the project. This paper analyzed and demonstrated the cross section shape in the reservoir area after the ultimate capacity formed based on the balance principle of silting and scoring, optimized the original dredge program in accordance with the principle of the range covered by sediments under the cross section contour of the ultimate capacity and reduced the amount of dredging significantly.