Abstract: Three-dimensional steady and unsteady numerical simulations were carried out for a fan with tandem cascades at design rotation speed. The matching characteristics of the tandem cascades and the corresponding rotor were emphasized. Detailed analysis of the fan flow field led to some preliminary conclusions:the matching characteristic of the tandem cascades and the corresponding rotor is bad near the hub region,resulting in serious airflow separation at the suction surface of the front tandem blade at the root region and big flow loss of tandem cascades. The total pressure loss of the tandem cascades is about 0.147 at design point and 0.215 at near stall point. The loads of the tandem cascades fluctuate intensely with the influence of the corresponding rotor wave.