The invention discloses a refrigerant control device and heat exchanging system and a control method of the refrigerant control device. The refrigerant control device comprises a valve body, a valve assembly, pistons and a formed refrigerant channel; when a refrigerant is throttled, a second valve port is closed through the piston under pressure gradient force of the refrigerant, and the gap between a valve needle and a first valve port is enlarged or narrowed to adjust the flow quantity of the refrigerant; an outlet and an inlet of the refrigerant are exchanged, the second valve port is opened through the piston under the differential pressure of the refrigerant, and the refrigerant conducts direct flowing, so that throttling or direct flowing is adopted according to the system application requirements, the volume is small, and system arrangement is simple.