To simulate the coupling behavior of member subjected to variable axial force and bi-bending,the multi-spring model is applied widely.Author has presented an improved model which considering the plastic stiff influence of plastic-region shear deformation in other paper.The simulation precision not only depends on the element model but also closely relates to two important parameters: the layout of spring and length of plastic region.Paper focuses on the two parameter analysis and puts forward reasonable suggestions.At last,paper also offers the appropriate spring layout to simulate the residual stress.