In research of overlay networks, simulator takes a very important role. However, popular simulators, such as ns and PlanetLab can't meet the scale and performance requirement of overlay research. Although it is necessary for overlay researchers to observe activities of million nodes, current simulators can not give such simulation result. To improve the overlay network research efficiency, we design and implement ONSP, a novel parallel overlay network simulation platform, which provides parallel discrete event simulation of overlay networks on high performance cluster. With this tool, we are able to build overlay network simulator in large scale easily and test it in short time. The test result proves that ONSP can well address the requirement of performance and scalability. Keywords overlay network, discrete event simulation, parallel