On the experiment of inertial confinement fusion,the success of implosion experiments is depended on the irradiation uniformity. In order to improve the uniformity of laser imtensity,time smoothing technologies are always applied with spatial technologies. Technology of smoothing by spectral dispersion is one of the familiar time smoothing technologies,and spectral broadening is the core technology. To improve the effect of spectral broadening,a double-pass phase modulator which would meet the need of spectral broadening of technology of smoothing by spectral dispersion is designed instead of the old single-pass phase modulator. The matching condition under double-pass modulator is calculated theoretically,and a satisfying result is also attained in the experiment,so the feasibility of double-pass phase modulator is validated. Based on the above discussion,another idea of multiple-pass phase modulator is mentioned.