In light of the change of the inertia of the slewing in a large range and the existence of unknown disturbances, for the speed control system of hydraulic hybrid excavator slewing, a robust controller was designed by using hybrid hydraulic drive technology, and its effectiveness was validated after correction of the system. A robust H∞ controller was designed based on linear matrix inequality (LMI). The actual controlled object was converted to an extensive controlled object by choosing the suitable weighting function of matrix. Then a robust controller was designed which met requirements in performance. The simulation results show that the designed controller system has greater stability and robustness, can effectivly resist parametric disturbance and interference, which satisfying the desired performance requirements of the system.