In order to select right direction of defense, the paper studies the issue of selecting defense directions in the smokescreen air defense based on TOPSIS. Considering the tactical game between the two sides, the paper constructs the matrix game which reflects the fierce rivalry of interest, and achieves comprehensive sequence of the defense direction by the TOPSIS, and finally uses a new decision thinking to establish the decision-making support model of selecting main defense direction in the smokescreen air defense. Meanwhile, the numerical examples and a case are given to illustrate the effectiveness and practicability of the improved model. Simulation results show that the research can supply the computer-assisted decision support for selecting main defense direction.