In recent years, the infrared camouflage characteristics of spray have been studied widely, but there is few researches on the relationship between the characteristics of water mist and the SNR of missiles. Aiming at this problem, on the basis of the comprehensive analysis of water mist against infrared imaging missile complex process, the simulation model is established. Computer simulation experiment is carried out through the mathematical model of the interference effect. Based on the Mie theory, the relationship between the different characteristics of the spray and the signal-to-noise ratio of the missile is given, and the influence of different characteristics with the consequence of the experiment is analyzed.