Abstract This paper makes use of mobile gravity observation data of Guangxi and its neighboring regions from 2014 to 2017, systematically analyzing the change in the regional gravity field, as well as its relationship with the July 15, 2017 MS4.0 earthquake in Nandan, Guangxi. Combined with GPS observation data and investigation results of seismology and geology, it explores the temporal and spatial distribution characteristics and the mechanism of the change in the regional gravity field. The results show that: (1) before and after MS4.0 earthquake in Nandan, the abnormal change in the gravity near the earthquake area is closely related to the main fracture in space, which reflects the crustal deformation and tectonic activity along controlling earthquake fracture that caused the change in the earth's surface gravity from 2014 to 2017; (2) the dynamic image of the differential scale gravity field better reflects the gravity variation near the epicenter before and after Nandan MS4.0 earthquake, and it is a system evolution process from “abnormity of local gravity→ characteristic abnormity of four-quadrant distribution→reverse change earthquake-triggering”; (3) gravity change and horizontal motion reflected from GPS observations suggest that Nandan MS4.0 earthquake is located in the distribution center of gravity four-quadrant and near the peak of surface compression, and this observational fact further supports that the dynamic changes in gravity field and deformation field have implications for the prediction of locations of moderate-strong earthquakes; (4) the area of Tian'e-Nandan-Huanjiang is the most gravitationally-evolving area and it is also a surface compression transition zone of horizontal deformation. At the same time, it is located in Moho surface and other deep-line intensely changing sections, ML3.0 earthquake encircling area, and abnormal b value area along main fracture. Combined with the images of seismic activities and the comprehensive analysis of observed anomaly of fixed-point precursors, it is considered that there still exist a danger of moderate-strong earthquakes in this area.