It is impossible to implement all-weather infrared stealth of a ship by using a coating with a changeless emissivity. Taking the radiation contrast less than 0.04 of a target and the background as a judgment criteria, the variation range of the target surface emissivity required for infrared stealthy is obtained by calculating and analyzing the infrared characteristic models of the target and background. A method for changing the average surface emissivity of a target by using electrochromic materials is proposed. Compared with the common infrared stealthy coating with a fixed emissivity, the stealthy efficiency of the infrared stealthy coating with a changed emissivity is improved greatly. It can meet the all-weather infrared stealth requirement of a target basically.