A favorable flow field enhances the product transport capacity and also increases the electrochemical mass transfer rate. In this paper, an end-side connected electrode suitable for electric arc electrochemical composite milling was proposed based on the existing flushing form. The aim is to simultaneously enhance the machining of the groove surface and the side. The flushing form was optimized by the flow field, and it was shown that the internal flushing increased the area of the high flow rate zone of the bottom gap. In the experiments, it was found that the internal flushing reduced the secondary discharge probability, the accumulation of re-solidified material on the groove surface was decreased, and the surface dissolution was uniform with low oxidation. However, the central jet is lost along the course and a zero velocity zone exists at the corners of the groove. Therefore, the sidewall open flow field is proposed to reduce the sidewall recast layer. It was verified that the sidewall slots of the positive flow type improved both the surface quality of the groove surface and the side wall. It was also found that the increase in the number of open grooves facilitates the generation of uniform debris removal. Display omitted •A gas-liquid-solid three-phase flow model was developed for flow field optimization.•The flushing form was optimized and the important role of internal flushing was demonstrated.•An end-side connected electrode with improved surface and sidewalls quality was proposed.•The optimized end-side connected electrode can be adapted to more complex working conditions.