This paper implements the model transformation between the Unified Modeling Language (UML) and the Enterprise Process Modeling System (EPMS). Modeling is the feature of UML, which is mainly used to describe software. A UML model can not be simulated and optimized. EPMS, which supports simulation, analysis and optimization, is applied to build and simulate business process models. Model transformation needs to create the corresponding rules. The idea of ontology is used to describe rules, which separates the program of rules from the mapping program and implements the decoupling between mapping and rules. The source model converts to a target model through the mapping program based on ontology rules. The experts of a field can manage, maintain and modify ontology rules, which reduces the workload involved in the mapping program maintenance by professional programmers.