Abstract: Different principles are applied to critical load computing problems about variable cross-section compression bars, and the stable equation for first-order critical load is converted into difference equations. Making unknown deflections of discrete coordinate points and critical load of compression bars to be design variables, the construct objective function based on the relation is satisfied by nonlinear difference equations. The optimization algorithm of critical load analysis and solution for variable cross-section compression bars are put forward. The generalized program is designed to solve the critical load of a variable cross-section compression bar. By the analysis and comparison of practical computing examples, it is proved that the algorithm is simple in program design, high in precise and fast in convergence. The method can be well used in engineering.