Taking electrochemical machining plane as an example, the relationship between machining gap and machining current in electrochemical machining was obtained through theoretical and experimental research, and a gap control system based on current signal was proposed to obtain the motion state in the process of machining in real time. The system collected the electrical signal of the sampling resistance in the process of processing and outputted it to the control module; the signal was compared with the set value in the single chip microcomputer program to make appropriate processing, and combined with the relay, the signal was sent to the NC system to realize the control of machining gap. The experimental researches on NC electrochemical machining plane under two kinds of gap control states were carried out. The results show that under the gap control state, the machine tool energy consumption is low, the machining process is stable and reliable, and the surface quality is good.