The invention relates to an evaporation fan used for a vehicle air conditioning system, which comprises a volute base, impellers, a motor assembly and a volute upper cover. In the evaporation fan, a centrifugal type biaxial fan is adopted; the biaxial fan is fixed in a screw rod propelling mode; the biaxial fan is fixed inside an installation chamber of an air conditioning (HVAC) assembly with wedge nuts and opening pins by a screw rod; the volute base is an assembly base framework of a fan structure; the motor assembly is fixed in a hemicycle recess in the middle of the volute base; a first impeller and a second impeller are fixed on two extending axle ends of the motor through an interference assembly; a wave filter is fixed on the two sides of the recess of the volute base through self-tapping screws and encases the other edges of a motor excircle; and the volute upper cover is fixedly arranged on the upper ends of the impellers through the self-tapping screws and forms an air ductof the fan with the volute base. The fan has the advantages of low noise, convenient installation and maintenance, reduced total installation time and labor intensity, and improved fan efficiency.