Abstract: The traditional truss optimal design methods can hardly satisfy the strength requirements at both component-and system-levels simultaneously. In order to overcome this problem, an improved method of uniform bearing criterion was proposed for the optimal design of two-level strength of steel trusses using the elastic modulus reduction method, considering the effect of structural stability. Firstly, the stability coefficient was introduced into the sectional compressive strength for components of steel trusses, so that the element bearing ratio was developed for elements of a steel bar under the influence of structural stability. Then, the strength coefficients at component-and system-levels were determined respectively, using the component bearing ratio in the first and last iterative steps of the elastic modulus reduction method. The relationship between the two-level strength coefficients was presented explicitly. Furthermore, each component strength was adjusted in terms of prescribed targeted two-level strength coefficients, while the convergence criterion was proposed for the trusses optimal design based on the uniformity of component bearing ratios. Finally, it was demonstrated that the proposed method obtained a design scheme for steel trusses with lower cost, overcoming the limitation that the traditional optimum methods cannot meet the requirement of two-level strength.