Ocean buoys generate six degrees of freedom motion due to the influence of marine dynamic environment, which can affect the reliable operation of observation platform and instruments, and even lead to measurement results errors, affecting the safety and data quality of ocean buoys. Therefore, the accurate measurement of buoy motion is of great practical significance. This article establishes a hardware system by integrating a micro inertial measurement unit with a global navigation satellite system to obtain buoy motion-related data. A carrier phase smoothing filter model is used for data preprocessing, and a least squares redundancy algorithm is fused to calculate the buoy attitude data, obtaining high-precision dynamic buoy attitude. After comparing the results of a swaying platform simulation of motion, the root mean square error of attitude angle is less than 0. 5°, and the root mean square error of horizontal velocity is less than 0. 05 m/ s. Additionally, through practical sea trials experiments, especially during the passage of a typhoon, the test results show that the system works stably and reliably without divergence phenomenon, with over 95% overall valid data.