In electrochemical microdrilling (ECMD), the machining accuracy will be affected by stray current. The most effective improvement is to coat the insulation layer on the electrode sidewall so that current can only be accurately released from the bottom end. In this he electrode is coated by using the sol-gel dipping method. The innovative oxygen plasma surface treatment is used to improve film adhesion on the helical edge. The electrode has voltage resistance up to 19.4 V by oxygen pressure of 400 mtorr and plasma power of 40 W. Finally, the coated electrode is tested to know the ECMD performance. The objective of this paper is to enhance the machining accuracy for ECMD process. The process parameter P44C01E could obtain effective improvement on difference between inlet and outlet from 157 μm to 10 μm.