On 28 March 2025, a M7.9 earthquake struck Myanmar, causing substantial casualties and widespread building collapse. During the rapid post-earthquake assessment, the estimated number of fatalities was generally overestimated. To investigate the causes of this discrepancy, this study examines two critical components of rapid fatality assessment: the delineation of seismic intensity zones and the estimation of fatality rates. First, the factors leading to overestimation of both the affected intensity area and the associated fatalities are systematically analyzed. Subsequently, based on 31 sets of detailed fatality data obtained from field investigations in Myanmar, country-specific parameters in the global empirical fatality estimation model are recalibrated. Comparative analysis indicates that the original model tends to underestimate fatalities in low-intensity zones while overestimating fatalities in high-intensity zones. Validation results show that the revised model provides estimates that are more consistent with observed conditions in Myanmar, thereby offering a reliable reference for improving future rapid earthquake fatality assessments in the region.