In order to judge the pressure bar without buckling and ensure the effectiveness of conventional force analysis，some conditions to be meet for the pressure bar under enough strength were studied, and the concept of “relative buckling length”that is the corresponding length of bar for a certain type of section steel was defined when the pressure stress was up to the yield limit by applying the buckling characteristics theory of pressure bar. Then, the relative buckling lengths of three main sections, such as square tube, angle steel and channel steel, were calculated by the parametric design function of the finite element analysis software Workbench 12.0 combining with the buckling theory in the material mechanics. The results show that when the length of the practical pressure bar is less than the relative buckling length, only the integral component can meet the strength requirement without considering the buckling of the practical pressure bar. Conversely, even if the strength of the integral component is sufficient, the buckling analysis of the pressure bar is required separately to ensure the overall stability. With this conclusion, calculating the relative buckling lengths of all specifications of section steel and designing the parameters of selected section steel and components can reduce the workload of the conventional design and ensure the structure safety of the mechanical equipment.