Abstract: To accurately analyze the mechanism of impacts of particles on rocks during partical impact drilling and to optimize hydraulic parameters, it is necessary to perform theoretical calculations of particle impacting depth. Based on dynamic spherical expansion theory, correlation between resistance and intial incident velocity was derived. From differential equations of particle motion, the calculation model for the particle impacting depth was established. In addition, definite solution conditions and relevant algorithm were clarified. Based on actual calculation, the correlation between impact depth and incident velocity and that between the impact depth and time were studied. Experimental results showed theoreticalresults match well with experimental one. So the theoretical model can be used in theoretical analyses of particle impacting processes. Research results demonstrated that the dimensionless rock breaking depth would increase linearly with the the initial incident velocity and would increase logarithmically with time. Relevant research conclusions may provide necessary theoretical support for the application of particle impact drilling techniques.