The invention relates to a single water evaporation air conditioner. The air conditioner comprises an upper cover, a fan, a water distribution pipe, a humidifying screen, an inlet air filter screen, a base, a water tank, a water pump, water supply and return pipes and an electric control device, wherein the water distribution pipe and the humidifying screen are in a ring-shaped structure, the water distribution is arranged on the humidifying screen, the fan is arranged at the center of the base, namely in the ring formed by the water distribution pipe and the humidifying screen, the humidifying screen is arranged in a ring-shaped groove of the base, the base is surrounded by the inlet air filter screen, the water supply and return pipes are arranged among the water distribution pipe, the base and the water tank, and the electric control device is connected with the fan and the water pump. The air conditioner has the following advantages: the structure is compact; a periodic water supply and return mode to guide return water; and the base is integrated with a concentration cavity, a water collecting tank structure and related pipes, thus cost is reduced. The single water evaporation air conditioner can be widely applied to the roofs of various vehicles and watchhouses.