<p>A system coupling model was constructed, incorporating the piston, reversing valve, cylinder, accumulator, drill rod, power source, and impact device, to analyze the dynamic performance of the gas–liquid combined hydraulic impact hammer. The model, developed using AMEsim, analyzed the oil pressure states in key chambers and the motion state of the piston. Moreover, dynamic performance experiments were designed, and the accuracy of the system coupling model was verified. The evaluation indices for dynamic performance included the peak pressures in the front chamber, back chamber, signal chamber, and return pipe, as well as the piston’s maximum impact velocity, impact energy, impact frequency, and impact power. Furthermore, the effect of piston clearance on dynamic performance was analyzed, providing a reliable foundation for the design and performance evaluation of the gas–liquid combined hydraulic impact hammer.</p>