The invention relates to a double-tunnel complementary type ventilation system and an air duct fire smoke-mixing prevention device, and belongs to the technical field of highway tunnel ventilation andfire protection. The double-tunnel complementary type ventilation system comprises a horizontal complementary air duct used for communicating two adjacent tunnels and the air duct fire smoke-mixing prevention device used for control of opening and closing of the air duct; the air duct fire smoke-mixing prevention device comprises a controller, a fire detector, a fireproof door, capable of openingand closing, arranged on the side wall of the air duct, a door retaining appliance for retaining the fireproof door in an open state to be opened, and a door closer; and the controller is used for outputtingcontrol releasing signals to the door retaining appliance when the controller receives the detected signals, indicating the occurrence of a fire, output by the fire detector. Through the air duct fire smoke-mixing prevention device is added in the horizontal complementary air duct, the horizontal complementary air duct used for communicating the two adjacent tunnels can be quickly closed when fire occurs in the tunnel, thus secondary disasters caused by smoke-mixing are reduced, and the air duct fire smoke-mixing prevention device can be widely applied in the field of tunnel engineering.