Abstract: It is analyzed that why jaw triangular tooth and trapezoidal tooth structure of the output shaft of the piercing mill gear reducer has so short a service life.Accordingly the improvement approach is proposed through relevant strength calibration and finite element analysis(FEA), i.e., changing the component material, enlarging the general contact area, and changing the output shaft connection type, etc.Based on the analysis it is concluded that with the same structural dimensions, both the loading capability and stability of the toothed coupling are less than those of the involute spline coupling;and that coupling with the spline made of 30Cr2Ni2Mo steel shall remarkably prolong the service life of the foresaid component, and thus enhance the productivity of the mill.