The simplest transmission structure of the motor directly connected to the impeller consists of components such as a current collector, main body, and diffuser. Adopting a new type of high-efficiency wing shaped twisted blade, with adjustable installation angle, and installing a stabilizing ring device to ensure that the aerodynamic performance curve has no hump, the base can be equipped with axially movable wheels. Therefore, it has the advantages of high efficiency, low noise, wide coverage, stable performance, simple structure, easy installation, and convenient use. The DK40 and DK45 series main fans are connected by two K40 and K45 fans of the same model and power, and the two-stage impellers rotate in opposite directions to form a counter rotating structure. Compared with the long axis transmission type main fan, they have the advantages of high operating efficiency, low operating resistance, and saving civil engineering investment, and have significant energy-saving effects.