The invention discloses a movable type on-line cleaning system for a circulating cooling water heat exchanger. The system comprises the heat exchanger, a heat exchanger water outlet gate valve, a centrifugal pump, a water storage tank water inlet gate valve, a water storage tank, a water storage tank water outlet gate valve and a heat exchanger water inlet gate valve which are sequentially connected to form a circulating loop. A dirt discharge tank is connected between a pipeline between the heat exchanger water inlet gate valve and the water storage tank water outlet gate valve and a pipeline between the centrifugal pump and the water storage tank water inlet gate valve through pipelines. A first valve with a flange and a second valve with a flange are arranged at the two ends of the dirt discharge tank respectively. A branch pipe with a third valve with a flange is arranged on a pipeline between the heat exchanger water inlet gate valve and the water storage tank water outlet gate valve. The tail end of the branch pipe is connected with an air compressor. The dirt discharge tank and the air compressor are arranged on a cleaning vehicle. The problem that regular stop of work and production is caused by a cleaning mode in the prior art is solved through an uninterrupted cleaning mode, three-phase cleaning is formed through crushed ice and high-pressure gas, and secondary scaling formed by dirt deposition in traditional chemical cleaning is avoided.