To address the scientific challenges in laboratory shock testing of large-inertia and large-scale marine structural components, particularly those used in deep-sea naval environments, a pneumatic-hydraulic shock testing apparatus (PHSTA) has been developed. In contrast to conventional drop-weight, pendulum, or explosion-based shock simulators that rely on localized collisions or rigid impacts, the proposed PHSTA employs a pneumatic-hydraulic spring mechanism to provide controllable, repeatable, and tunable shock responses. A comprehensive theoretical framework was developed, including dynamic modeling of the PHSTA, energy storage analysis, and closed-form expressions for equivalent stiffness and acceleration characteristics. The effects of gas precharge pressures p_0 and loading pressures \mathrm{\Delta }p on the stored energy E, shock acceleration, and the system’s dynamic characteristics—in particular the natural frequency and damping ratio—were quantitatively analyzed using AMESim. Experimental validation was conducted on a prototype PHSTA, and the measured shock responses demonstrated the validity of the proposed model, showing good agreement with both the theoretical analysis and simulation results. At p_0=10 MPa, the peak acceleration increased by 24.7% compared to p_0=13 MPa, closely matching the simulated result of 23.3%. The developed PHSTA offers a novel approach for simulating marine shock environments under laboratory conditions and provides a robust platform for evaluating the shock resistance of offshore and naval structural components.