Abstract: Accurately identifying of pre-seismic ionospheric electromagnetic anomalies is a pivotal challenge and a primary step toward overcoming the bottleneck of short-term earthquake prediction. Using the electric field data in the Very Low Frequency (VLF) band provided by China’s first electromagnetic monitoring satellite (CSES-01), this study investigates the the electromagnetic anomaly associated with the Mw 7.0 Mexico earthquake that occurred on 8 September 2021. We employ the Empirical Mode Decomposition (EMD) method combined with the multiple entropy-based approaches (sample entropy, permutation entropy, fuzzy entropy, energy entropy, time-frequency entropy, multi-scale entropy and their combinations)—to decompose, reconstruct, and extract anomalous signals from the power spectral density data of the VLF electric field. The results show that, after excluding the influence of space weather activity, all entropy-based methods consistently detected significant disturbances of the electric field in both the seismogenic region (9.1°N, 22.69°N) and magnetic conjugate area (approximately 41°S) prior to the mainshock (i.e., on July 16, August 5, and August 15,). These disturbances exhibit hemispheric conjugacy features consistent with pre-seismic electromagnetic coupling. Although different entropy methods exhibit slight variations in anomaly response relative to background and clarity of anomaly boundary, their results demonstrate good consistency, indicating the effectivness and robustness of this proposed approach in identification of pre-seismic electromagnetic anomalies, and highlighting its potential for operational application in satellite-based seismic-electromagnetic monitoring.