Abstract: Micro-electro-mechanic system (MEMS) gyroscope is an emerging inertial sensor. However, the MEMS gyroscope could be affected by external perturbation during fabrication faults and field application, thereby reducing the detection accuracy of angular rate. Focusing on the constant element of unmatched perturbation, we propose a sliding mode controller based on the nonlinear perturbation observer to deal with the effects of constant unmatched perturbation. The unmatched perturbation can be estimated by the NPOB in real time, and a compensation factor is utilized in control law to improve control precision. The reachability of sliding mode surface and the convergence of the observer is analyzed and proved by Lyapunov's direct method. Simulation results show the validity and effectiveness of the proposed strategy.