In order to calculate the deployment distance between fire unit and its protected object or the distance between different fire units for the reef air defense, deployment distance models of reef anti-aircraft fire unit were built. Based on the small size of reef and its area depth limit to fire unit deployment, distance calculation model of the fire unit to its protected object was given. Due to the limited number of air defense force on the reef, killing depth and cover width of fire units were focused on. The deployment distance of fire units was analyzed and modeled based on constraints from the depth and width of the killing zone. Calculation example shows that the models can provide decision support and enhance the scientificness of air defense deployment.