Currently, wireless networked control system (WNCS) has become a hotspot in Internet research. Research on WNCS always needs simulation to verify the validity of the theory and methods proposed. Therefore, designing an excellent simulation platform for WNCS is very necessary. The simulation of WNCS involves control system and network environment, hence a cosimulation platform for WNCS over MANET is proposed in this paper. This cosimulation platform not only combines the network simulation software OPNET and the control system simulation software MATLAB/Simulink, but also includes MANET routing protocols, which carries out the cosimulation of control system and wireless network under the frame of network protocols. Finally, the effects of packet loss rate to the performance of WNCS are analyzed by the simulation of a single inverted pendulum WNCS to verify the effectiveness of this platform.