The distribution of earth pressure behind the retaining wall is an important basis for the design of wall shape and reinforcement. In order to study the distribution law of earth pressure behind the retaining wall under dynamic compaction, the physical model tests of the retaining wall under self-weight, heap load and dynamic compaction load were carried out. Through the monitoring of earth pressure at different depths, the influence of the tamping drop distance and the number of tamping on the distribution of earth pressure behind the wall was analyzed, especially the influence effect of dynamic compaction on the loose area. Based on the equivalent static method, the theoretical calculation formula of earth pressure behind the wall under dynamic compaction was modified. The results show that the soil pressure behind the wall increases instantaneously to the extreme value and then gradually decreases to stability under single tamping. With the increase of tamping times, the soil gradually becomes dense, and the corresponding soil pressure behind the wall increases gradually. The shallow soil will form the impact loose zone under the action of dynamic compaction. The soil in the loose zone becomes loose and the soil pressure value is small. The soil pressure in the lower part of the loose zone will increase rapidly and then decrease, showing a “bulging” nonlinear distribution. The soil gravity in the loose area and the thickness of the loose area, especially the latter, have great influence on the theoretical distribution curve of the soil pressure behind the wall. The modified theoretical formula of the equivalent static method of the soil pressure behind the wall considering the influence of the loose area is more in line with the actual situation.