A further research of the user-defined function in PSS/E is made. The requirements of environment, format and invocation of PSS/E’s user-defined function, user-defined modeling principle based on equivalent current injection as well as its implementation method which utilizes the coordinated call models are introduced. And the research is exemplified by modeling a user-defined static var compensator (SVC) model. Then an auxiliary signal control is appended to the user-defined SVC to improve whose transient performance in dynamic simulation. Through the comparison of dynamic simulation results, the feasibility and expandability of the proposed user-defined SVC model is validated. The user-defined modeling method proposed can be a guidance for modeling other complicated devices in PSS/E.