Through study of the rule of the air current between the metro stations which had installed the safety door system and the tunnel, this text established a physics model and a mathematics model, gained the mix coefficient which can marks the degree of the influence stopcock wind in metro inflict to the heat environment, exerting reasonable assumption and simplification, making use of the CFD imitation, adopting tracer air. The text elected three kinds of safety door system with different height to simulate and compare, gained the exact value of the mix coefficient, and simulated the energy consumption of subway air conditioning in different height of safety door by the mix coefficient.