A practical calculation method of considering the P-Δ effect is introduced. According to the lateral frame, the calculation model and the action load of calculating the P-Δ effect are established. The model characteristic is that the shear force of the lateral displacement member is statically, and the internal force of the first-order analysis is the same as the original structure. The effects each other of each column in the same layer are analyzed, the equivalence coefficients of embodying the P-Δ effect are deduced, the nonlinear analysis becomes the linear analysis. The internal forces are calculated by using no-shear moment distribution method.