In recent years, many e-auction marketplaces have been built and some of them provide similar e-auction services. The sellers and buyers who want to trade via online auctions then have the opportunities to compare and select a marketplace to trade. Therefore, the marketplaces compete with each other to attract participants. This paper proposed a simulation approach for studying suc hcompetition between marketplaces. We consider one simple scenario with two competing marketplaces and built the simulation model. This model is implemented within a simulation framework, which is designed and can be applied to many other models generally. Simulation experiments are configured and executed afterwards. The experiment results works not only as a proof of concept, but also confirms theoretical results. The simulation approach proposed in this paper enables a novel way for analyzing the competition among eauction marketplaces, and such approach can be easily applied for a wide range of competition scenarios between e-auction marketplaces.