Abstract: A speed regulation strategy for cycloidal rotor engines（CRE） was proposed, integrating an extended state observer（ESO） with sliding mode control（SMC）. The rotational speed was regulated by SMC with disturbance bounds, and the ESO was employed to provide real-time estimation of speed control errors and compensate for disturbances, thereby improving the accuracy of speed regulation. An equivalent model of the cycloidal rotor engine was constructed using GT-POWER and integrated with the control strategy in MATLAB/Simulink for combined simulation. Results demonstrated that under startup conditions, the overshoot in rotational speed was reduced to 22.6 r/min, representing decreases of 68.1%, 56.9%, and 29.4% compared to those of the conventional proportional-integral-derivative（PID）, fuzzy PID（F-PID）, and radial basis function neural network-based PID（RBF-PID） controllers, respectively. Under load conditions, the maximum negative deviation in speed control was 59.1 r/min, and the control performance was improved by 26.9%, 17.9%, and 13.8% compared to those of the PID, F-PID, and RBF-PID, respectively. During world harmonized transient cycle（WHTC） transient testing, the SMC-ESO strategy achieved the lowest mean absolute percentage error of 4.8% in speed control, which was 2.7, 2.2, and 0.9 percentage points lower than those of PID, F-PID, and RBF-PID, respectively. The findings validate the effectiveness and superiority of this control methodology in the context of cycloidal rotor engine speed regulation.