Abstract: To learn the distribution of the position of brine intrusion in the study area, the stratified monitoring and sampling of groundwater at the front line of brine intrusion are carried out respectively in dry season and wet season of a year, the water chemistry and stable isotopes of the groundwater are detected and the spatiotemporal variations of inert tracers and reaction tracers are analyzed. The results indicate that the spatial distributions of the brine/saltwater intrusion show that the correlation between the shallow surface groundwater and the brine intrusion is poor, the brine intrusion occurrs mainly in the shallow and middle groundwater aquifers, and the degree of the intrusion is relatively weak in the deep groundwater. The layer position of the brine intrusion varies in different regions. In the Mihe River Alluvial Fan the brine intrusion occurs in the shallow surface and shallow layers, in the Weihe River Alluvial Fan it occurs in the medium deep layer and in the Bailang River Alluvial Fan the position of the intrusion is not obvious. In the horizontal distribution, the layer of brine intrusion is thin in the south, brine occurs in the middle and seawater is distributed in the north. The freshwater samples exhibit a phenomenon dominated by brine intrusion in the mid-to-deep layer. The brine intrudes in a wedge-shaped form along the layer. Locally, there is a certain degree of overflow intrusion. that is, the lower underground saltwater intrudes into the upper underground freshwater. From the perspective of the temporal distributions, the brine intrusion shows a wedge-shaped trend in the vertical direction in dry season, whereas in wet season the freshwater in the major intrusion layer of 20–50 m thick is advanced towards the shore and the shallow and deep intrusions are still ongoing, with the degree of the deep brine intrusion being even higher. This study can further deepen the understanding of brine intrusion in the Weibei Plain and suggests that in order to further explore the periodic law of the hydrogeochemical characteristics of brine intrusion, it is necessary to carry out long-term hydrogeochemical stratification monitoring.