Abstract: In order to accurately evaluate the static strength and fatigue strength of the boom structure, it is necessary to obtain accurate finite element simulation stress. The finite element models of ZL50 loading motor arm structure without weld and with weld were established respectively in this article. Based on the fatigue test attitude, loading mode and constraint form of loader working device, the influence of mesh size and modeling mode on the static characteristics of the boom structure was studied. The results show that the smaller the mesh element size of the finite element model is, the greater the structural stress of the boom will be, but the stress changes will gradually converge and stabilize. Compared with the finite element model without weld mesh element, the stress value in the high stress region of the plate connection area is reduced, but the stress value in the low stress region is basically the same. The research results would provide analysis basis for fatigue life evaluation of the welded structure of the loader.