Based on TE₀₁ circular electric mode， the elliptical quasi-optical mode converter is studied， and a modified formula for rapidly designing elliptical-structure quasi-optical system is proposed. The quasi-optical system designed by the modified formula is composed of an elliptical Vlasov launcher and a quasi-paraboloidal mirror. The simulation results show that the beam launched by the elliptical system has the characteristics of better launcher directionality and lower side-lobe gain， and its size is smaller than the traditional circular system.