In order to improve the infrared stealth of water surface object, the attenuation character of water spray on infrared radiation was numerically investigated. The infrared attenuation and temperature response of the composite test board were measured before and after the water sprayed. The numerical and experimental results show that water spray with a certain concentration can decrease infrared transmission efficiently and change the infrared radiation feature of the test board quickly. According to the detective model of infrared system, the detective distance and image distance were analyzed with and without water spray between infrared imager and water surface object. The analysis result demonstrates that the detective distance of water surface object decreases about 25% and image distance decreases about 19% after water spray system was turned on, which tells that water spray is an effective method for infrared stealth and it can be widely used in the infrared stealth of water surface object.