This paper proposes a 3D finite element mechanical calculation model of tower-line coupling system. Based on the analysis of the displacement and stress distribution of the strain section that under wind and icing condition, the safety margin curve under definite ice thickness and wind speed condition is proposed. As a result of calculated and verified the weak tower and weak elements of the tower, the characteristic of the weak position distribution is obtained. A working transmission line which happening a tower collapse accident is the subject investigated. The application of the mechanical calculation results to analyze the optimizing scheme of the operational transmission line, the methods that replace the steel type of the tower weak elements and add a tower in weak position of the strain section are proposed. Both the comparison critical curve of the strain section and the comparison curve of the tower weak elements stress ratio demonstrate the validity of the improved corrective recommendations.