Abstract: This paper aims to study the seawater intrusion problems in the sandy aquifer, and determine the development and evolution of saltwater-wedge in the aqueous medium through the seawater intrusion process. It simulates seawater intrusion process in the soil bin, using the high-density resistivity probe observing system to remote and real-time monitor the vertical resistivity changes of the soil through the seawater intrusion process. It determines the development of the seawater intrusion by analyzing the resistivity data. The result shows that the high-density resistivity probe is good at monitoring the occurrence and development of seawater intrusion. The formation of the salt-fresh mutation interface, the evolution of the transition zone and the change of salt-fresh water interface are monitored. The high-density resistivity probe is sensitive to the change of seawater interface. It is useful to real-time monitor and pre-warning the seawater intrusion.