PID (Particle Impact Drilling) is a new drilling technology which has been developing in the near decades. Utilizing steel particles with high speed to impact the rock stratum, this technology could be used in hard terrane. Compared with ordinary drilling technologies, PID has many advantages, such as long service life, high drilling speed, and low duty cycle, etc. During the process of recycling and separating, the steel particles will inevitably encounter a part of loss. In order to keep the sum of steel particle and working efficiency, the loss rules should be intensively studied. Based on experimental studies, this paper mainly works on the screening efficiency under various conditions including volumetric flow rate of drilling fluid, viscosity and steel particle ratio, etc. It was found that the loss rate of steel particle would increase with the increasing volumetric flow rate, viscosity and steel particle ratio. Furthermore, dimensional analysis was employed to analysis the relationship between loss rate and these factors and one empirical formula was proposed.