A technique of fast ellipsometric measurements based on dual-drive elastic modulation is proposed in paper, for which the measurement speed of traditional mechanical rotary compensator ellipsometer is slow. The modulation mode of 45°dual-drive photoelastic modulator (PEM) working in pure traveling wave mode was studied by theoretical analysis and simulation. The results show that the fast axis direction can high-speed periodic rotation and the phase delay is constant when the PEM working in pure traveling wave mode. Combined with the principle of ellipsometry,a theoretical model of fast ellipsometric measurement based on dual drive PEM was studied in detail. The results show that the optical period of this model was less than 10μs, and the ultra-high speed optical modulation could be realized.With this study, it is expected to solve the problem of ultra-high speed detection of thin films in the production process of semiconductor integrated circuits, microelectronics and photovoltaic cells. It is of great significance and academic value for in-line measurement of thin films.