The invention discloses a fluid reversing switching valve for an ultrafiltration device. The fluid reversing switching valve comprises a cylinder body, a first actuator, a first end flange, a first piston rod, a first switching valve piston, a second actuator, a second end flange, a second piston rod and a second switching valve piston. Through the control of the main valve body, bottom filtration, bottom washing, bottom backwashing, top filtration, top washing and top backwashing of the ultrafiltration device are realized. In the ultrafiltration system, a total water inlet control valve, an upper water inlet control valve, a lower water inlet control valve, an upper water discharge control valve and a lower water discharge control valve are avoided so that system operation and control complexity caused by too many valves in the ultrafiltration system engineering project is reduced. The invention also provides a fluid reversing switching method for an ultrafiltration device.