Abstract: In order to reduce the impact of ejector system exhausts on the optical transmission, design method of emitting exhaust gas to the outside of optical transmission area is proposed. Fluid characteristics for exhaust pipe in ejector system and the influence area of exhausted gas are studied using numerical simulation methods. Based on the comparison results of flow field characteristics of straight pipe and elbow bend pipe, design manners of exhaust pipe which satisfies the engineering requirement are proposed. Under the condition of having no natural wind or having the side toward natural wind, the influence districts of exhausted gas are confirmed by the multiple species transport models with the fixed exhaust velocity of ejector system, and according to the influence area of exhausted gas, the pipe length and arrangement style are discussed.