The occurrence of qty calculation for revolver structure is widespread in breakwater project, and the section-centroid method is one superior solution. This essay proves the dependability of this method firstly, analyzes its restricted scope and structure, the program to locate centroid point and the method to ascertain density of sections after that, and finally demonstrates its application and superiority with a actual project. This method can increase the calculation efficiency notably, decrease approving time, and create project benefit having the aim of computer program.