The energy loss of the impact mechanism of hydraulic rock drill greatly affects drilling efficiency when it operates.In this paper, the major energy loss of hydraulic impact mechanism was analyzed in theory, and a calculating formulae of the energy loss was deduced, which is of guiding importance to the design of hydraulic rock drill. The theoretical analysis has shown that there are a group of oil sealing lengths and movement journey of vale core of distributing valve to reduce the energy loss to a minimum for a certain powered hydraulic rock drill.Through the energy loss calculation of impact mechanism of an example hydraulic drill, the design parameters of its impact mechanism were optimized, resulting in that the energy loss of its impact part and distributing valve decreases 1.74% and 10.67% respectively.