Abstract: Device for enhancing efficiency of air-conditioner, including a water reservoir, a water level sensor, a controller and a water-injecting section. The water reservoir receives the condensed water produced from the water exhaust of the vaporizer of the air-conditioner. The water level sensor is disposed in the reservoir for real-time sending water level signal to the controller for judging whether water should get into the water reservoir or discharge therefrom. The controller is able to detect the operation state of the compressor of the air-conditioner to activate the water-injecting section to inject water onto the heat-radiator at proper time so as to continuously decrease temperature of the heat-radiator and the air therearound and enhance efficiency of the air-conditioner and avoid load loss due to high temperature of the components of the air-conditioner after long period of operation.