Abstract: Disclosed is a reduced-pressure type backflow preventer comprising a valve body (1), two check valves (2) of the same structure and a drain valve:(3) wherein a cavity is formed body, and a valve wall of the valve body is provided With a water inlet, a water outlet, and a drain opening; the two check valves are both fixedly mounted inside the valve body supporting member (4), and are positioned at the water inlet and the water outlet, respectively; the drain valve is mounted outside the valve body, and is positioned at the drain opening; the check valve comprises a valve seat (201), a valve clack (202), a rocking bar (203), and a twin torsional spring (204); one side of the valve clack is hinged to an upper end of the valve seat, and the other side is provided with a roller (205); the rocking bar is connected to a lower end of the valve seat via a pin (206); the roller abuts against the rocking bar and slides on the rocking bar; the twin torsional spring is sheathed over the pin; and a spring force of the twin