In order to improve assembly efficiency, a fast and lightweight assembly system is developed based on CREO Parametric three-dimensional modeling software. The lightweight model is generated by extracting the surface of the component model. The one-to-one correspondence between the lightweight model and the vertices, edges and surfaces of the component model is established by model parameters. The lightweight model is used to replace the component model for assembly. The automatic mapping of the entity model is carried out from two aspects: mapping of space position and mapping of assembly constraints. The analysis results show that the method can meet the needs of rapid and lightweight assembly, and automatically map the lightweight model under the lightweight machine model to the solid component model.