In order to verify the principle of the prototype design plan of the crown mounted semiactive drill string heave compensation system, cosimulation models of the pneumatichydraulic circuit and multibody mechanical system were built based on the multidisciplinary simulation software SimulationX. The dynamic response analysis was carried out for the compensation system under three working conditions of passive heave compensation mode, active heave compensation mode, and hydraulic medium leaking mode. Simulating results show that the compensation accuracy, pressure fluctuation of the accumulator and hydraulic cylinder structure stability of the crown mounted semiactive compensation drill string heave system achieve the design goal and meet the standards requirements. The system can maintain compensation function at a small amount of hydraulic medium leakage and meet the requirements of related rules of classification society. The simulation and analysis results provide reference for development of the crown mounted semiactive drill string heave compensation system in our country.