The field detective results and the laboratory testing results are given for the silty soil foundation of the flood-prevention dyke in Yibin strengthened by dynamic compaction method. The field detective data of the strengthened foundation show that the valid strengthened depth is about 8 meters by the 1600kN•m compacted energy. The test site is compacted with 2 times of full compaction at the space of 5 meters and another low energy compaction at the space of 2 meters. The dry densities of the subsoils are increased and the compression and permeability are decreased through dynamic compaction. The standard penetration numbers are all more than 7 while there are 32.2% of the standard penetration numbers less than 5 for the natural subsoils. The subsoils can meet the need of the requirements in bearing capacity and settlements of the flood-prevention dyke after dynamic compaction. The liquefaction tendency at the 7 degrees of earthquake has been disappeared through the dynamic compaction. The equilateral triangle arrangement of the compacting points is better than the square arrangement of the compacting points through the dynamic penetration tests and standard penetration tests.