摘要：Small-sized axial fans are used as air cooler for electric *** there is a strong demand for higher power of fans according to the increase of quantity of heat from electric ***,higher rotational speed design is conducted,although,it causes the deterioration of efficiency and the increase of ***,the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of *** the case of contra-rotating rotors,it is necessary to design the rotor considering the unsteady flow condition of each front and rear *** the present paper,the fan performance of the contra-rotating small-sized axial fan with 100mm diameter at a designed and a partial flow rates is shown,and the unsteady flow conditions at the inlet and the outlet of each front and rear rotor are clarified with unsteady numerical ***,the relation between the performance and the unsteady flow condition of the contra-rotating small-sized axial fan is discussed and the methods to improve the performance are considered.