Aiming at the wild used tide gauge, a research project has been made. The purpose of the project is to build a standard test equipment which is used for calibration. The principle of the tide gauge is imitating water-level fluctuation of diurnal tides or semi-diurnal tides, based on controlling dynamic water flow which is 10 meters high and 8 tons heavy. This is a national standard test equipment which will be used by Tianjin National oceanic standard measuring center. In this paper, the digital PID control method is used for computerizing servo motor .First, the principle of servo motor control has been discussed, and then PID adjusting theory and method are also introduced. At the same time, software compiled is used to control servo motor. In the end, the corresponding results can be output on the hardware platform. The method above has been proven advisable.