In order to accurately and effectively realize the geometrical element error modeling of parts, a geometric element error modeling method based on multi-tolerance coupling is proposed in this paper. Small displacement torsor (SDT) was adopted to describe the tolerance, and the geometric element error model for the translation of the translational tolerance and the fixed tolerance was established. By using the failure rate p of the constraint equation, the actual distribution of the parameters of each error component was derived and the geometric element error model was built. The method was extended to the assembly error modeling of complex assemblies by using the Jacobian spin model, realizing the prediction of assembly accuracy. The rationality and feasibility of the method are verified by the prediction of the assembly accuracy of the top tailstock.