During the micro-electrical discharge machining (micro-EDM) process, the dielectric property of narrow interelectrode gap is transiently changing. With the hysteretic servomotion of spindle, the effective discharge ratio (EDR) between electrodes is low. In this research, a pulsed power supply superposed with the radio frequency (RF) oscillating wave of controllable frequency and amplitude is proposed in order to induce interelectrode continuous discharge, so that, the machining efficiency and accuracy are improved simultaneously. The experimental results of microhole machining show that under the oscillating frequency of 160 MHz and amplitude of ±10 V, the machining efficiency is increased by 35%, the tool electrode wear rate (TWR) remains almost unchanged, and the taper error of microhole is reduced by 43%. Furthermore, the process of relatively enlarging discharge gap range and increasing number of discharges after superposition is discussed, and the proper superposed oscillating amplitude is identified.