Use of out of tolerance in hanging rail construction in engineering machinery usually causes inadequate utilization of the material and results in waste. Based on a mechanical analysis of the main beam structure in track hanging, a design optimization problem of weight of the girder structure is transformed to a solution of optimal parameters values under mechanical constraints optimal parameters. Using a girder flange plate and the web geometry value as input parameters, structural strength, stiffness, stability as response parameters, an optimization model is established based on a zero-order algorithm. Optimization results of the main beam are obtained by finite element numerical calculation. The results show that the new design method can reduce weight of the main beam and improve the efficient use of materials.