In order to accurately and effectively realize the geometrical component error modeling of parts, a geometric component error modeling method based on multi-tolerance coupling is proposed. The method uses Small Displacement Torsor (SDT) to describe the tolerance, and establishes the geometric element error model for the translation of the translational tolerance and the fixed tolerance. By using the failure rate p of the constraint equation, the actual distribution of the parameters of each error component is derived. Regularity, the geometric element error model is established. The method is extended to the assembly error modeling of complex assemblies by using the Jacobian spin model, and the prediction of assembly accuracy is realized. Taking the prediction of the assembly accuracy of the top tailstock as an example, the rationality and feasibility of the method are verified.