The distribution of infrared signatures of exhaust gas device on ships is studied numerically. A numerical model which considers the participating gases is established to predict the distribution of infrared signatures. The results of numerical prediction are reasonable and creditable compared with the experimental results obtained by foreign counterparts. The model established is simple and elective. With the help of this model,we can design a reasonable geometry Of exhaust gas device to reduce the maximum infrared signature intensity and improve the living ability of warships.