Based on the mode coupling theory, the design of TE01-TM11 mode converter geometry configuration with traditional waveguide axis constant curvature and improved waveguide axis sinusoidal curvature Was presented for more acceptable geometry parameters. More considerations were given to the influences of muhimode factor, backward wave, ohmic losses carried from metal wall and phase rematch. The conversion efficiency of Ka waveband with waveguide axis sinusoidal curvature is about 99% with bandwidth of 32%. At the same time, the relation among the radius and curvature of circular waveguides, the length of converter and converting efficiency is obtained.