The design and establishment of focus servo module in the hybrid magneto-optical recording system are presented. The servo module, which acquires focus error signal through astigmatism method and utilizes the double-laser method integrated with red-laser servo and blue-laser assisted recording, serves as an independent dynamic focus servo unit. Thus, with the feature of modularization and palatability, the servo module can be used in both stable and dynamic laser recording system, in both horizontal type and vertical type optical system. For control algorithm design, the amplitude-frequency and phase-frequency characteristics and the nonlinear hysteresis of PZT are studied in detail. High accuracy dynamic focus servo is realized through PI closed-loop control with the inverse system and inverse hysteresis model calibration. Focus error is within ±130 nm under the rotate speed 8 r/s, and the diameter and depth of recording spots are almost uniform.