In order to guarantee the safety design of the sea launch platform during offshore thermal launch and make clear the supersonic heat flow impact on the offshore support platform during the thermal launch, a numerical model for the wake from the rocket motor with four nozzles is found. The distribution of the fluid temperature, pressure and speed are calculated at different distances from the nozzle to the deck of 5 m, 10 m and 15 m. The simulation results show that the distance from nozzle to deck is of important influence on the wake shock structure, when the distance exceeds 10 m, the temperature and pressure of the wake decline sharply. The simulated results are of great reference value on the safety design of the offshore launch platforms and innovation of the diversion device structures.