This paper has developed a new-type groundwater dynamic auto-monitoring system based on Smart Device. The system adopted Smart Device as host computer of data acquisition, used Windows Mobile which was prevalent operation system of Smart Device now, software development environment Visual Studio.NET 2003, and C# as the developing language based on .NET framework. It adopted serial port RS232 as the communication interface between Smart Device and monitor host machine and utilized multi-threading design to achieve serial port communication. It adopted the standardized and textual XML to store the data. And this system implemented the function of data acquiring, file managing, and analysing and displaying. In virtue of fully considerations in characteristic of Smart Device, this system had the succinct window interface, simply operation, powerful function, and was very convenient to carry. Moreover it has already made very good use result in practice.