Dynamic compaction is a widely used method for subgrade treatment due to its merit. This article presented example of dynamic compaction test in a liquid foundation project and investigated the relationship between settlement, ground heave and drop counts, the relationship between horizontal displacement and depth of soil, the relationship between drop counts, depth, horizontal displacement and pore water pressure, and the relation curve of pore water pressure and time during single point impact test. According to the conclusion before and after the testing, some appropriate engineering parameters were obtained and some advices were put forward.