Considering the insufficiency of numerical study on the percussion characteristic of hydraulic rock drill, which restricts the improvement of efficiency and reliability, a coupling model including the impact piston, spool valve, impact accumulator, and connecting pipelines was established taking into account the oil compressibility, oil leakage, and pressure drop in valve ports. The rebound velocity of impact piston was calculated based on the stress wave theory. The simulation results revealed the coupling mechanism of percussion system. Pressure curves of the piston’s front-chamber and rear-chamber, and valve’s left-chamber and right-chamber were obtained by field rock drilling test. Then, the velocity curve of impact piston was obtained after judging the striking point through the feature of rear-chamber’s pressure spike, so were the rock drill’s impact energy, impact frequency, and impact power. The simulation and experimental results have consistency. And, on this basis, the influence of spool valve’s damping clearance ( δ ) and pipeline diameters ( d 1 , d 2 ) connecting the impact piston and spool valve on the percussion performance and system cavitation was researched. The results show that the larger δ is better considering reversal time of spool valve, the impact frequency of rock drill, pressure fluctuation, and cavitation relief. But too large δ will cause over quick impact velocity of the spool valve, which may lead to strong vibration and the damage of spool valve. The optimal value of δ is 0.01 mm by comprehensive consideration. The pipeline diameters have an important influence on the pressure fluctuation and negative pressure in rear-chamber. The diameters should be larger than 18 mm to alleviate the cavitation. This article provides means for the design and research of rock drills.