Abstract: A fine calculation method was proposed on key weld according to sub-model technology. This method aims to solve the problems of inaccuracy and low efficiency in the calculation of key weld of long boom concrete pump truck turret. Firstly, the overall calculation and analysis of the turret were carried out to evaluate the regional stress of turret key weld. Secondly, the sub-model of the key weld area of the turret was established, and the weld model was established according to the actual parameters in the sub-model. Then, the stress distribution of the sub-model under different grid element sizes was calculated, the stress convergence was analyzed, and the reliability of the sub-model cutting boundary was verified. Finally, the key weld parameters were optimized, the calculation results before and after optimization were compared to verify the feasibility of the optimization scheme, and the optimized parameters were applied to the actual production of the key weld of the turret. The results show that the application of sub-model technology to check and evaluate the key weld of the turret can significantly improve the calculation efficiency and accuracy of the weld, and provide scientific basis for the optimization design of the weld parameters. The research results provide a feasible and effective method for weld design of turret, and also provide an important reference for local structure calculation of other large structural parts.