Abstract: Aiming at the problems that the variable angle mechanism of generalized ellipsometer is mostly driven by dual motors, and has complex structure as well as deviation of optical path after angle variation, a new variable angle mechanism of generalized ellipsometer driven by single motor was proposed. A fixed polarization generation arm was adopted by the structure, which was driven by a single motor geared by the synchronous gear to rotate the loading platform and the polarization detection arm synchronously, so as to realize the multi-angle measurement of the ellipsometer. On the basis of the traditional horizontal variable angle mechanism of the generalized ellipsometer, the 1 : 2 synchronous transmission of loading platform and polarization detection arm was set up, and the feasibility of the structure was verified by Inventor motion simulation. The proposed single motor driven variable angle mechanism not only maintained the collimation before and after the angle variation, but also had a simple overall structure, which greatly optimized the complexity of the ellipsometer angle variation, and had an important application value in the engineering process of the generalized ellipsometer.