<p>Fast EDM (electrical discharge machining) drilling is widely used in the machining of film cooling holes of aero-engine turbine blades. However, the EDM process will produce a recast layer, which will affect the surface performance of blades. Therefore, there is a need to explore the mechanism by which process parameters of fast EDM drilling can affect a recast layer. In this paper, the effects of process parameters on the recast layer thickness are studied in detail according to the electrical parameters (pulse-width-time (Ton), pulse-off-time (Toff), average current (Ip), capacitance (C), etc.) and machine tool parameters (flushing pressure (P), tube electrode diameter (D), tool electrode rotation speed (n), etc.) of the high-speed electric spark small hole. According to the formation mechanism of the recast layer, the reasons for influences of different parameters on the recast layer are explored from a theoretical level, and the range of process parameters is selected according to actual machining conditions. Through the control variable method, the influence rules of various process parameter variables on the recast layer are explored one by one, and the variable parameter simulation is carried out by using a thermal-fluid coupling model, and the mathematical formulas of different process parameters affecting the recast layer are derived, respectively. Combining the variable parameter simulation results and mathematical theory, the mechanism of different process parameters on the recast layer thickness is explored.</p>