In order to truly reflect the characteristics of the flow field of the engine tail flame, take certain type carrier rocket as example, numerical simulated its flow field. Using computational fluid dynamics (CFD) method, as three dimensions dual nozzle engine for the model, considering the tail flame mixed gases composition including hydrogen, carbon monoxide, carbon dioxide and water vapor in working condition, simulate the flow field simulation of the carrier rocket launch, analyze the near-field plume flow shock wave system structure and the parameter distribution, etc. The analysis results show that each parameters distribution and shock wave structure under mixed gas are consistent with the theoretical analysis results, the distances from the center of the nozzle on the ground 1 m location by the maximum pressure, about 0.4 MPa, the highest temperature is in the center of the two nozzle which is about 2 700 ℃, provides reference for subsequent related experimental measurement and theoretical basis.