Abstract: A diagonal flow fan includes an air duct, a motor, a fan wheel, a blade, an air guiding ring, and a wheel hub, the air guiding ring has one end connected to the air duct, and the blade and the wheel hub are located inside the fan wheel, the blade has one end connected to the wheel hub and another end connected to the fan wheel, wherein the motor is located inside the wheel hub and connected to the wheel hub, the air guiding ring has another end located at an inner side of the fan wheel, and a gap exists between the air guiding ring and the fan wheel.