The rigidity enhancement effect of the integral gusset plate is often simulated in the calculation of an integral nodal steel truss bridge by using a beam element with a rigid arm to improve the calculation accuracy.By taking Zhongshan Lianshwan Bridge as the engineering background，an optimization method based on a multi-scale truss model for nodal rigid domain simulation was proposed and verified.Five consecutive standard sections were selected as the study objects，and the beam element model with rigid arm and the multi-scale model of gusset plate substructure were established by using Ansys.The same boundary and loading conditions were applied.The deflection of the main truss of the multi-scale model was used as the target deflection，and the deflection of the main truss of the beam element model with a rigid arm was fitted to the target deflection by changing the length of the nodal rigid arm.The length of the nodal rigid arm was substituted into the whole bridge model for subsequent calculations after the deflection was fitted，which optimized the length of the nodal rigid arm.The three models before and after optimization were calculated and analyzed for the construction process and bridge state.The comparison between the finite element calculation results and the measured data shows that the theoretical deflection after optimizing the nodal rigid domain is always in good agreement with the measured data，and under the maximum cantilever condition，the theoretical maximum deflection of the nodal domain is only 26.6% of the rigid domain，while the theoretical maximum deflection without considering the influence of the rigid domain is 124.1% of the measured value.The error is smaller than that under the overestimated rigidity，which indicates that the optimized model simulates the actual rigidity of the bridge better，while the error caused by the inaccurate simulation of the nodal rigidity enhancement effect may be larger than the error of ignoring the rigid domain.