The invention discloses a water purifier special for a water resource heat pump system. A driving device is arranged at the top of a barrel body (1), the bottom of the barrel body (1) is supported by a stander (10), the barrel body (1) is provided with a rotational cartridge filter (4), and washing and filtering are performed simultaneously through a filtration piloting device and a washing device of the rotational cartridge filter (4). The device is searched and developed for the water resource heat pump system, and is mainly used for the water resource heat pump system to filter silt, floater, particles, and the like in river, lake, sewage, and other water quality. The filter surface of the water purifier rotates, and part of the filter surface is positioned in the back washing area at any time with constant filter function. The sand-carrying capacity after filtration of the device is less than one in 200,000, and the use of a water resource heat pump assembly is satisfied. The water purifier back washed by used purified water is not blocked and scaled. The water purifier has small occupied area and does not need a person to specially manage.