With the advancement of the “Dual Carbon” initiative, the proportion of renewable energy integrated into power grids continues to increase. However, the characteristics of low inertia and low damping in such systems pose significant challenges to grid stability. To address these issues, grid-forming Virtual Synchronous Generator (VSG) control has been widely adopted to simulate the dynamic behavior of synchronous machines. This paper proposes an improved VSG control strategy that integrates impedance reshaping and sliding mode-enhanced Active Disturbance Rejection Control (SM-ADRC), aiming to overcome the limitations of traditional VSG, such as complex parameter tuning and inadequate disturbance rejection capability. First, a grid-connected VSG system model is established, and its operational principles are analyzed. Then, the virtual inertia and damping coefficients are reshaped in the frequency domain to enhance transient performance. Furthermore, a sliding mode control-based ADRC is designed, using angular frequency as the input to generate compensatory torque for improved dynamic response. Finally, MATLAB/Simulink simulations are conducted to evaluate the proposed method. The results show that the improved control strategy effectively suppresses power and frequency fluctuations and significantly enhances the transient stability of the grid-connected system under various disturbance scenarios.