Abstract: In the outlet of the fan and the interior of the air\|cooling cell, the flow field may become more realistic because of the introducing of the tangential velocity. Based on the proportionally reduced model for the representative air\|cooling fan of 600MW unit, a tangential velocity function which is changing with the radius of the fan blade is presented. The physical and mathematical models for the air velocity fields about the operation of the nine fans were established. The similarities and differences of the flow fields are obtained through CFD simulation after the tangential velocity is introduced. The results show that the flow field will change greatly after the tangential velocity is introduced, so this condition should not be ignored in the CFD simulation. And it is useful for the optimal designing of air\|cooling island.