The invention relates to an improved bypass valve (10). The bypass valve is suitable for connecting a feeding pipeline with a returning pipeline of terminal devices and heat transfer fluid. In the terminal devices, heat exchanging is conducted between the to-be-adjusted environment and the heat transfer fluid; and the terminal devices are typically limited by a heat exchanger, a draught fan plate wire unit and a battery of an AHU type air conditioning unit in the HVAC field. The bypass valve comprises an H-shaped valve main body (12) provided with two pipe-shaped elements arranged oppositely and parallelly. The two pipe-shaped elements arranged oppositely and parallelly limit a conveying guide pipe (14) and a returning guide pipe (16) which are connected and communicate with each other by a transverse element for limiting a bypass guide pipe (18). An opening-closing conveying valve, an opening-closing returning valve and an opening-closing bypass valve are integrated into a single body structure through the valve main body, and moreover the opening-closing bypass valve is provided with a linear lock gate (43) for allowing/preventing the heat transfer fluid to circularly pass/from circularly passing the bypass guide pipe (18).