A polarization-independent phase-only Liquid Crystal (LC) phase retarder was demonstrated by using two orthogonal identical Liquid Crystal Variable Retarders (LCVR). Based on Jones matrix theory, the relationship of polarization state between input beam and output beam was deduced. And the Stokes parameters were measured on the condition that the voltage individually applied to the two LCVRs was 1.55 V and 1.49 V. It is proved that the structure well operates in polarization-independent modulation. And the phase variation induced by voltage from 1~2.7 V is given out.