A solution based on center frequency control is proposed for dual phot oelastic modulators to solve the problem of low modulation efficiency,which is caused by differences o f eigen frequency and their variation with temperature.First,a circuit is established to equalize the mechanical properties of photoelastic modulator.And the dynamic coupling relations between driving frequency. driving voltage and resonant frequency are analyzed.Then,according to the amplit ude-frequency and phase-frequency curves of photoelastic modulators with different eigen frequ encies,a control method for dual photoelastic modulators is presented based on center frequency.Finally, direct digital synthesis and digital phase locked loop are used to drive the dual photoelastic modulators and track the resonant frequency drift,so as to keep the photoelastic modulators synchronous in fre quency and phase.Experimental results show that the control method can double t he optical path difference compared with the single photoelastic modulator.