About 50 km away from Dayawan Nuclear Power Station, a M_L4.6 earthquake occurred at the Shanwei-Chaozhou fault on 11 March 2022. There was an earthquake as large as M6.0 occurred in same site. In this paper, based on the geomagnetic observation data of 10 geomagnetic stations in coastal areas of South China, the integration effect of the diurnal variation distortion period was used to quantify the distribution of anomalies.we discussed the degree of interference and the decisive factors in the calculation according to the prediction range of the day-to-day ratio threshold, and the internal source ring current is used as the source to explain the source current mechanism related to the geomagnetic day-to-day ratio anomaly. The results show that filtering the geomagnetic station data with large noise interference can effectively remove its noise, improving the credibility of the day-to-day ratio calculation. It is proposed that the diurnal variation amplitude of the geomagnetic vertical component is mainly controlled by the Sq current system, which may be related to the space weather activity of the ionosphere and is obviously dependent on local time. Estimating the skin depth of the current change in the three-layer conductor and combining with the results of other geophysical explorations, we believe that the position where the ring current is generated may be located at the most intense exchange between the asthenosphere hot material upwelling to the lithosphere material, about 100 km underground. Therefore, we calculate the induced magnetic field distribution caused by the ring current superimposed on the surface at a depth of 100 km. The magnetic field generated by this internal source current weakens the vertical geomagnetic field caused by the Sq current. Themagnitudeofthe Z-component changes day by day, which eventually leads to an anomaly in the day-to-day ratio of the geomagnetic field.