Abstract: Based on the principle of minimum potential energy, the indirect load effect matrix of a rigid frame is established. The transfer law of a constrain matrix due to transition form a stiff-joint to a hinge is deduced according to the property of the constrain matrix transformed from the indirect load effect matrix. Add the redistribution moment vector derived from the constrain matrix to an original moment vector, and the internal force of the new rigid frame can be obtained immediately. As the simplified method avoids rebuilding and decomposing the total stiffness matrix and the solution of joint displacements, the computation rate is greatly improved. The numerical examples show that the proposed simplified method is correct, reliable and effective.