An adjustment-free air curtain type ventilation cabinet comprises a cabinet body (15) and a column (16) provided on the cabinet body (15). A vertically movable window (18) is mounted on the column (16). An air curtain machine (19) is mounted at an upper end of the window (18). An air discharging duct (17) and an air supplementing duct (24) are mounted at an upper end of the cabinet body (15). The air discharging duct (17) is connected to an air discharging box (20). An upper end of the air discharging box (20) is provided with an upper air discharging port (23), and a lower end is provided with a lower air discharging port (21). An air blocking plate (22) is provided at a join between the air supplementing duct (24) and the cabinet body (15). A Venturi valve (7) is externally connected to the air discharging duct (17) and comprises a valve body (1). A rotating blade (2) and a ball (3) are provided in the valve body (1). The ball (3) is movably mounted on a fixed rod (4). A spring (5) is provided on the ball (3) and the fixed rod (4). The fixed rod (4) is fixedly provided on the valve body (1) by means of a fixed frame (6). The fixed rod (4) and the fixed frame (6) are fixedly connected to each other by a bolt. The ventilation cabinet produces a factory-configured volume of air, and delivers a completely constant air volume during use, meeting use requirements of a constant air volume ventilation cabinet.