The principle of repetition rate locking technology and the application background of a δ cavity SESAM mode-locked all polarization maintaining Er-doped fiber laser is introduced and a set of experiment device which can quickly lock the repetition rate of SESAM mode-locked all polarization maintaining Er-doped fiber laser is designed. The locking device will finally lock the repetition frequency of laser to the hydrogen maser, so that the stability of the repetition frequency of the fiber laser is the same as the hydrogen maser. The repetition rate stability of the all polarization maintaining Er-doped fiber laser is quantized by using the method of calculating repeated frequency Allan variance. And the stability of repetition rate is compared between the locked laser and the unlocked laser.