It is necessary to analyze the structural strength of the moving arm and make some optimization designs to reduce its weight. According to the actual structural sizes of the moving arm of a loader, we build its 3D mathematical model by bottom-to-up modeling method in ANSYS. Having considered bearing actual loads and displacement constraint conditions of a moving arm in actual working situations, we got the stress distribution rules and the destructible locations of the moving arm in a working cycle after analyzing the strengths of the moving arm in six different typical kinds of working conditions. Based on this, we made the design module and the structural optimization designs of the moving arm by using first-order method based on the objective function's sensitive degree to design variables in ANSYS software. The results of the study suggest that the maximum equivalent effective stresses in six different typical kinds of working conditions are all less than the admissible stress of the material of the moving arm, and the maximum bearing stress exists in the working condition with bearing unbalance loadings in horizontal and vertical directions. The advantage of the optimization design is outstanding with the 67% less of the maximum equivalent stress of the moving arm and 15.4% less of the volume.