[Objective] To address the issues of low-speed integral drift, high-speed parameter mismatch, and insufficient robustness of the traditional hybrid model flux observer (HMFO) in surface-mounted permanent magnet synchronous motors for new energy buses under complex operating conditions such as sudden load changes and wide-speed-range operation, this study proposes an improved HMFO control strategy that integrates closed-loop sliding mode correction and feedforward extended state observer (ESO) compensation. [Methods] Under the voltage-current hybrid model architecture, a compensated first-order low-pass filter cascaded with a high-pass filter was first employed to replace the pure integrator for the elimination of DC bias and integral saturation. Secondly, a closed-loop feedback with the active flux linkage difference between the two models as the sliding surface was constructed, and the error was driven to converge in finite time by using sliding mode control. Finally, an ESO was introduced to compensate for parameter perturbations and load disturbances in a feedforward manner, which effectively suppressed sliding mode chattering and improved steady-state observation accuracy. [Results] Simulation results showed that under sudden load change and speed step conditions, the peak speed errors of the improved HMFO converged to ±0.4 r/min and ±0.6 r/min, respectively, and the dynamic adjustment times were compressed to within 4 ms and 10 ms, respectively. The transient error peaks of the position angle were reduced to below 1.6×10-5 rad and 2.5×10-5 rad, respectively. No obvious high-frequency chattering was observed in the steady-state error, and the observation stability was significantly superior to that of the traditional scheme. [Conclusion] The strategy successfully balances high dynamic response and strong robustness, effectively overcoming the integral drift and saturation problems of traditional HMFO. Simulation results preliminarily verify the application potential of this method under complex operating conditions of new energy buses.