In response to the voltage stability problem of isolated microgrids under uncertain factors such as system parameter fluctuations and load changes, this study uses an optimized and improved extended state observer to construct a robust voltage sliding mode control scheme. This scheme incorporates the disturbance factors inside and outside the system into the aggregated uncertainty and constructs a state space representation model for islanded microgrids; A novel improved extended state observer is proposed based on a linear extended state observer, aiming to effectively estimate the uncertainty inside and outside the system. A sliding mode controller that integrates multiple order approximation characteristics is constructed to ensure that the output voltage of the system can quickly and accurately follow the set reference voltage, thereby significantly improving the overall robustness of the system. Through simulation and comparative experiments, it has been verified that this scheme can significantly resist internal and external disturbances in the system. Under diverse load conditions, it can quickly follow the reference voltage, ensuring good dynamic adjustment performance of the output voltage and steady-state operation. This confirms the effectiveness of the control strategy in practical applications.