Abstract: This paper analyzed the flux and pressure continuous characteristic of electrohydraulic servomotor airtight cavity. And an improved genetic algorithm involving the mechanism of simulated annealing was introduced to carry out the structure optimization for improving low speed performance. The formula of pretransitional curve of the stator and its angle range was derived, and the optimum dimension of triangle cushioning groove of the valve plate was also obtained. This optimization method perfectly combines the global optimal characteristic of genetic algorithm and the local optimal specialty of simulated annealing algorithm. The algorithm not only avoids premature convergence, but also makes the neighborfunction structure more reasonable. Applying this method to design the servomotor, the continuous rotary electrohydraulic servomotor can track the low speed ramp signal of 0.001 °/s and the tracking precision can reach the boundary of 0.001 °.