Change in the flow resistance coefficient of underwater hammers was analyzed through comparison of common types of hammers in multiple projects based on the LS-DYNA fluid-structure coupling numerical simulation method. The results show that, when the hydrostatic pressure on the bottom surface of the hammer is a fixed value, the flow resistance coefficient decreases with the increase of the hammer mass. The hammer fall velocity in the water increases with the drop distance, but the growth rate gradually decreases and tends toward a stable value. The energy usage ratio of the hammer decreases with the increase of the drop distance. When the hydrostatic pressure on the bottom surface is a fixed value, the energy dissipation rate increases with the decrease of the hammer mass.