Automobile cooling system fans have predominantly been axial fans, due to their low cost, thinness, and ease of mounting. However, since flow resistances in front and back of the fan are very strong, air tends to flow diagonally at the fan outlet side. The fan does not operate as an axial flow fan.In order to move towards the operation of an axial flow fan as a diagonal flow fan, this report introduces the idea of the diagonal flow design with an “aerodynamic diagonal flow hub”. In order to give this idea as broad an application as possible, we generalized from an obser-vation of the relation between design flow coefficient and operating range, and engaged in experimental studies, design, and prototype manufacture. In the end, we verified that the new design features have higher performance and lower noise than the ordinary axial flow fan.