An improved design method of transonic fan is presented. In order to control shock structure

migration of the low momentum fluid

and therefore to improve the performance of the transonic fan

the leading edges of sweep blades are considered as design freedoms in this method.Three high loaded transonic fans with low aspect ratio were used to prove the practicability of this method.The numerical study of the three transonic fans demonstrates the effect of the sweep leading edge on the flow field structure.