According to RTA operating map, a highly loaded single stage fan on low corrected speed and at various stator setting angles are simulated using threedimensional (3D) numerical simulation software NUMECA. The results show that under the condition of low conversion rotating speed in the highaltitude and at a highspeed, a partial fan passage is chocked up with flow and the increasing of the mass flow of fan is restricted due to the increasing negative angle of attack of blade loads. The negative angle of attack of blade is sensitive to stator setting angle. The adjustment of stator setting angle can partly restrict the negative angle of attack of blade and nearly remove the chock of fan passage, which loads the increasing of the mass flow and adapts the demand of the fan during wind milling.