Abstract: Initial prestress value is the key parameter when designing stayed steel column. Based on general mechanical model of stayed steel column, static equilibrium equation was introduced, further the relationship between optimum initial prestress and maximum critical load was set up. Based on complete buckling mode function, the equation of maximum critical load was founded with energy method, thus perfect theory on optimum initial prestess was achieved. Finally numerical analysis based on three models was performed to verify the precision of the proposed theory.