Abstract: The relative gravity data were calculated by the of classic adjustment from 2017 to 2019 in the North-South seismic belt. We analyzed the precision of gravity value at sites in the study area of south-east of Gansu province, and studied the variation of the regional gravity field before Xiahe Gansu M_S5.7 earthquake. The results show that ① Gravity value precision of 90% gravity sites is less than 10×10^-8 m·s^-2 after adjustment calculation in our study area, and the gravity value at absolute gravity sites is well accordance with absolute gravity observation. ② Between April 2017 and April 2018, gravity variation is positive in the south-west side of the Lintan-Dangchang fault, and it is negative in the north-east side of the fault. It is opposite to the gravity variation before Jiuzhaigou M_S7.0 on August 8, 2017. There are violent difference gravity variation in the area near the Hezuo city and Xiahe county. ③ Between April 2018 and April 2019, gravity variation is negative in the south-west side of the Lintan-Dangchang fault, about -10×10^-8～-30×10^-8 m·s^-2, and it is positive in the north-east side of the fault, about +20×10^-8～+30×10^-8 m·s^-2. The gravity variation is not obvious near the epicenter of Xiahe M_S5.7 earthquake, which indicated that the area near epicenter was possible to be in locked during the time. While there is a unconspicuous four quadrant distribution of gravity change centered on the junction of Xiahe county, Luqu county and Zeku county. ④ Strong earthquakes are prone to occur in four quadrant distribution center of gravity change of high gradient belt of positive and negative anomalies. We made a medium-term forecast about Xiahe M_S5.7 earthquake based on relative gravity changes, especially forecasting localities of potential earthquake.

Key words: 2019 Xiahe M_S5.7 earthquake, Gravity changes, Lintan-Dangchang fault, Precursor