A phase control method of femtosecond laser pulse pair over a large range is presented, which is based on the assumption that change of the laser polarization state affects the optical path difference factor of the two beams in the Michelson interferometer. Based on the phase locking of the two beams from the He-Ne laser, the relative phase difference control for femtosecond laser pulse pair is achieved over a large range. The dynamic phase locking for the beam from the He-Ne laser and the relative phase difference control for femtosecond laser pulse pair are validated experimentally. The former experimental result shows that the optical path difference of the two arms is controlled within nanometer scale. The measured autocorrelation curve of the femtosecond laser pulse fits the theoretical result well, and the Fourier transform shows a single-peak spectrum. The system can steadily achieve the relative phase difference dynamic control of the femtosecond laser pulse pair almost without limitation of range.