The accurate calculation of IR emissivity is the basis of modeling and analyzing the ship turbulent trailing wake in IR. Based on Cox-Munk probability distribution function(PDF) of slopes model, and corresponding to bi-directional reflectance distribution(BRDF) function of sea surface, a method for calculating IR emissivity of ship turbulent trailing wake in typical ocean environment was formulated. According to calculation, the emissivity distribution of typical ship turbulent trailing wake in 8-9 μm long-IR band for both small zenith angle of airborne detection and big zenith angle of shipborne detection were studied. The results show that the difference of emissivity between turbulent trailing wake and sea background is increased along with the detecting zenith angle. What′s more, the radiance of turbulent trailing wake of typical ship is calculated in cloudy autumn shipborne detection condition, which is compared with the sea trial data. The results show that in typical ocean condition, the radiance of turbulent trailing wake is lower than sea background, presenting the characteristic of "cold trailing wake".