For providing a good condition of measuring, the gravimeter gyro-stabled platform plays an important part in the gravimeter system. By adopting the pure-inertial and the all-digital controlling technology of real-time leveling, the gravimeter gyro-stabled platform will be directed primarily towards isolating the angular motion of the carrier, and keeping the sensitive axis of the gravimeter parallel with the plumb line all the time. In the sea condition, the gravimeter gyro-stabled platform has a low precision in the disturbing of low frequency of sea waves, this paper introduces a leveling algorithm based on Mixed Sensitivity. By adopting a reasonable leveling bandwidth, performance bound function, controller weighting function and bounded uncertainty function, we achieve an optimal control to the leveling loop via the algorithm.