GPS buoy is the important instrument for the calibration of altimeter sea surface height. This paper introduces the composition and operating principle of GPS buoy, and describes in detail the design of shape, cabin, leak-proofness, and current supply. And finally used the numerical simulation, the rock and undulation of GPS buoy were experimented in the 3 class sea state condition. The result shows that designed GPS buoy can meet the challenge of altimeter sea surface height calibration on the sea experiment condition.