Upright tube's six degrees-of-freedom are constrained by horizontal tube and diagonal brace at the coupler connection joint, the strength of such constrains is the key factor of the stable bearing capacity of the scaffold. To determine the efficiency of the constraints, single factor sensitivity analysis and eigenvalue buckling analysis methods are applied to measure each constraints' contribution on stable bearing capacity. The efficiency analysis results of their contributions indicated the constraint mechanism of horizontal tubes and bracing tubes. Reasonable effectiveness of six constrains is tentatively researched according to the published experimental data of couplers, and then a multi-parameter simulation method of semi-rigid node is proposed. The premise condition of the multi-parameter simulation method is validated by the comparison between the experimental loads and the the inner forces' calculating results of the couplers, in which effective length method and linear elastic second-order analysis method are adopted. Accompanying with the research of multi-parameter simulation method, some common deficiencies or limitations of ordinary methods which are based on single parameter assumption are listed and analyzed.