Abstract: The buckling reliability constraints of structural optimum design are dealt with simplified method. The expressions for the mean value and variation coefficient of buckling resistance are derived according to three types of cross section. An equivalent random variable is used to replace the product of component resistance and section area .The non-linear limit state equation is simplified as a linear equation. The substitution formulas are derived and the errors in the equivalent procedure are effectively eliminated. Four trusses have been calculated to test the theory and method. It is illustrated with the results that the method is convenient for engineering application and meets the precision needs.