In this paper，the Gaoyou-Baoying MS4.9 earthquake was analyzed by the geomagnetic harmonic wave amplitude ratios method. As the earthquake was an isolated seismic event，before and after which there were no other earthquake occurring in this region，and the distribution of geomagnetic observation stations was dense，there is an advantageous condition for the characteristics analysis of the geomagnetic harmonic amplitude ratio. The analysis results verify the former knowledge about anomaly characteristics of the geomagnetic harmonic amplitude ratio，that is，the anomalous characteristics of the earthquake mostly appeared in the twist-recovery process. The results also show that the observation stations close to the epicenter didn't show the same phenomena. The anomalous characteristics were different between the northern stations to the southern stations. The difference also existed between the long and short periods.