In order to solve the problems in the ultimate bearing capacity analysis of steel frames with rectangular sections，an appropriate generalized yield function of rectangular cross-section was selected through the control internal force analysis，and then the elastic modulus reduction method for the analysis of the ultimate bearing capacity of rectangular cross-section rigid frame structure was established through the homogenization． Firstly，the equivalent homogeneous generalized yield function was established based on regression analysis and fitting error analysis． Secondly，the element bearing ratio were defined based on the homogeneous generalized yield function，then，the elastic modulus reduction method was proposed for determining the ultimate bearing capacity of steel frame by strategically reducing the elastic modulus of the highly stressed elements to simulate the structural stiffness damage． Finally，the key internal forces of the plane and space steel frames were investigated by means of determining the internal force ratios，further，an exact homogeneous generalized yield function was determined，and the accuracy and efficiency of the proposed method was verified． The results show that the proposed method as a linear elastic iterative method has high accuracy and overcomes the limitations of the traditional nonlinear iterative method，which can achieve higher computational efficiency．