The existing iterative algorithm suffers from the low accuracy of the processed mirror surface and the error caused by the phase compensation when it is used to plan for quasi-optical mode converter mirror system.A method for constructing a fair mirror is proposed by the NURBS-surface algorithm.Then a quasi-optical mode converter for a conversion of TE6,2to TEM00 mode operating at 70 GHz is designed by the proposed algorithm.Experimental verification and calculation shows that the designed mirrors system ha...