To address the challenge of manually establishing error transmission relationships in assembly tolerance analysis, particularly when dealing with a large number of surfaces and the influence of assembly sequences, this paper proposes an MBD-based (Model-Based Definition) automatic assembly error modeling method. This approach enables the automatic modeling of error transmission relationships directly on the 3D model. Initially, an assembly relationship graph is constructed based on the actual assembly sequence of the product, which is used to store the assembly information between parts. Subsequently, a geometric feature localization relationship graph is established using GD&T (Geometric Dimensioning and Tolerancing) annotations on the 3D model, clarifying the datum-target relationships between feature surfaces. Together, these two graphs determine the error transmission graph. Then, based on the hierarchical structure of geometric feature positions, the geometric feature position transformation relationships on the error transmission graph are identified, facilitating the subsequent tolerance analysis using the Monte Carlo method. Finally, the accuracy and effectiveness of the proposed method are verified by comparing it with the modeling and calculation results of traditional methods. This method overcomes the complexities, potential errors, and disregard for actual assembly sequences inherent in traditional processes, enabling automatic modeling of error accumulation relationships.