An all-fiber optical path difference adaptive control method is proposed, and it has been successfully applied to the femtosecond fiber laser coherent polarization combination system. Field programmable gate array (FPGA) control circuit is used as the hardware foundation in the establishment of the optical path difference adaptive control system, and an effective control algorithm is designed based on the hill-climbing algorithm, which can successfully solve the disturbance problem between optical path difference adaptive control and phase-locked control. The experimental results show that the system can completely compensate the optical path difference drift in the range of ±60λ with good continuous working stability, which can meet the requirements of optical path difference adaptive control in the femtosecond fiber laser coherent polarization combination system.