Objective To simulate the pressure field for extracorporeal shock wave lithotripsy (ESWL) by attaching additional reflector with different angles at the side of the ellipsoidal reflector edge in the Dornier HM3 lithotripter. Methods Based on axisymmetric Euler equations and hybrid grid improved CE/SE numerical scheme, the pressure field of shock wave changed by the additional reflector in ESWL was simulated. Results Pressures of the additional reflector with different angles near the focus were compared. There were significant 50% increases of both the positive and negative pressure peaks in the pressure field as compared to ESWL without additional reflector. The peak pressures were gradually decreased with the reflector angle increasing. The peak pressure of 45° reflector angle was about 25% less than that 0° reflector angle. Conclusions At the initial stage of stone comminution, stones were broken into smaller pieces due to the more concentrated energy produced by the additional reflector, which could reduce the firing frequency to achieve the same or higher stone comminution efficiency. The numerical simulation results provide a reliable numerical calculation result and useful reference for the improvement and clinical application of ESWL lithotripter.