To better simulate external characteristics of actual grid using power quality testing supply, this paper proposes power quality simulation method based on equivalent model of power grid. In view of similarity theory, similarity degree d is proposed as an index to evaluate the similarity between power quality simulated by testing supply and the prototype. With regard to H-bridge cascaded inverter topology, voltage source virtual impedance control strategy based on repeated study control is also proposed in this paper. It can simulate external characteristics of actual grid in fundamental situation, meanwhile it embraces high credibility. Ultimately, feasibility of proposed control strategy and index is verified by simulation.