<p>In order to eliminate the recast layer and improve the surface quality of the holes machined by electrical discharge machining (EDM), a combined machining method is proposed which introduces electrochemical machining (ECM) to remove the recast layer formed on lateral side surface of the hole during EDM drilling. In this method, a cylinder with varying diameters is applied as electrode. The electrode with larger diameter (EDM electrode) is utilized for EDM drilling in deionized water, while the electrode with smaller diameter (ECM electrode) is employed for ECM process in NaNO₃ solution to dissolve the recast layer. The purpose of using electrode with smaller diameter during ECM is to increase the gap between two electrodes by reducing the diameter of the electrode, preventing the generation of sparks in ECM process, and consequently it will not damage the surface quality and machining accuracy of the hole. The experimental results demonstrate that this new method can not only enhance the surface quality without compromising the accuracy of the hole, but also improve the taper of the hole when the diameter of ECM electrode is appropriately chosen. At the beginning of this research, the hole processed by this new combined method is compared with that processed by merely EDM in terms of surface morphology and element composition. Following that, the influence of three crucial processing parameters on the machining quality of the hole, namely the diameter of ECM electrode, the conductivity of NaNO₃ solution, and the processing time of ECM is analyzed through experiments. Ultimately, in order to remove the recast layer accurately, the model is developed and validated experimentally.</p>