To study the bearing capacity of soft soil reinforced by dynamic replacement method with various hammers, a calculation model was put forward for evaluating the soft soil's ultimate bearing capacity. A series of model tests was conducted to investigate the shape characteristics and the failure mode of the replacement piers. Based on the model test, the ultimate bearing capacity of replacement pier was established using the energy method, which was calculated using the GA_PSO optimization algorithm on the Matlab platform, and a parametric study was conducted to investigate the factors that influence the ultimate bearing capacity of the replacement pier. The test and calculation results show that the replacement pier is typically formed as a cone with cross section of an inverted trapezoid and the pier usually has a mode of bulging failure in the ultimate state. The diameter of the pier and soil strength around the pier have significant effects on the ultimate bearing capacity, which is consistent with the design concept of the dynamic replacement method with various hammer. The proposed method was verified to be feasible through comparison between calculation results and field test results.