In this paper, we propose an integrated approach to analysis and evaluation for STEP-based (STandard for the Exchange of Product model data, officially ISO 10303) electromechanical assemblies. First, two assembly representational models are brought up and elaborated: the EXPRESS/XML schema-based model and the NIST object-oriented UML-based open assembly model (OAM). Then, these two models are integrated, in which the OAM incorporates the EXPRESS/XML schema-based assembly model to completely capture the detailed geometric information. The proposed assembly evaluation approach uses the EXPRESS/XML schema-based model as the information source, and covers not only the geometric and physical characteristics of assembly parts but also the assembly operation data necessary to assemble the parts. The feature of this approach is the linkage of the STEP product definition to the fuzzy analytic hierarchy process for assembly evaluation. The proposed approach has the flexibility to be used in various assembly methods and different environments. A case study shows the feasibility of the proposed approach.