An expansion tank, comprising a cavity structure and a degassing flow channel, wherein the degassing flow channel is arranged in the cavity structure of the expansion tank, a plurality of flow guide holes are provided on the degassing flow channel, and the degassing flow channel is in communication with the cavity structure by means of the flow guide holes; a liquid inlet and a liquid outlet are provided at two ends of the degassing flow channel respectively, and the liquid inlet and the liquid outlet are used for being in communication with a vehicle cooling system; a filling port is provided at a top of the cavity structure of the expansion tank and used for filling a coolant; and the expansion tank further comprises a pressure regulating device used for regulating internal pressure of the expansion tank, wherein the pressure regulating device is a pressure relief valve arranged on an upper portion of the expansion tank or an air pump, the air pump is provided outside the expansion tank and in communication with the cavity structure, the air pump is regulated by a pressure sensor that is provided in the expansion tank, and gas discharged out of the coolant in the degassing flowing channel enters an upper space of the expansion tank and can be vented via the pressure regulating device, characterized in that the degassing flow channel is an independent pipe of a tubular structure provided at the bottom of the expansion tank, the flow guide holes are provided on a surface in contact with the expansion tank, and the expansion tank is in communication with the degassing flow channel by means of the flow guide holes, the degassing flow channel is detachably connected to the cavity structure, and the degassing flow channel comprises a flow channel body and a detachable cover plate. the degassing flow channel is arranged in the cavity structure of the expansion tank, a plurality of flow guide holes are provided on the degassing flow channel, and the degassing flow channel is in communication with the cavity structure by means of the flow guide holes; a liquid inlet and a liquid outlet are provided at two ends of the degassing flow channel respectively, and the liquid inlet and the liquid outlet are used for being in communication with a vehicle cooling system; a filling port is provided at a top of the cavity structure of the expansion tank and used for filling a coolant; and the expansion tank further comprises a pressure regulating device used for regulating internal pressure of the expansion tank, wherein the pressure regulating device is a pressure relief valve arranged on an upper portion of the expansion tank or an air pump, the air pump is provided outside the expansion tank and in communication with the cavity structure, the air pump is regulated by a pressure sensor that is provided in the expansion tank, and gas discharged out of the coolant in the degassing flowing channel enters an upper space of the expansion tank and can be vented via the pressure regulating device, characterized in that the degassing flow channel is an independent pipe of a tubular structure provided at the bottom of the expansion tank, the flow guide holes are provided on a surface in contact with the expansion tank, and the expansion tank is in communication with the degassing flow channel by means of the flow guide holes, the degassing flow channel is detachably connected to the cavity structure, and the degassing flow channel comprises a flow channel body and a detachable cover plate.