In the past few decades, precursor materials were used to the short-term earthquake tracking and annual meeting, and rarely be used for medium and long-term analysis. Base on some existing research results and related earthquake preparation theory model, we analyzed the trend turnings changes in 108 groundwater data. We choose 72 stable trend turnings with duration more than three years, and analyzed the space and time characteristics of those trend turnings according to the turning point in time and form. The data time series were divided into two periods at the year of 2000. According to the group characteristics of trend turnings of groundwater and cross fault leveling data of the north-south seismic belt in two periods, we found that the tectonic stress state in north of north-south seismic belt was enhanced after 2000, and it was a relative relaxation before. The results of this paper could provide some references for the future judgment to the earthquake activities in the north-south seismic belt.