There is micro discharging gap to be measured between negative electrode and positive electrode in precise micro electrical discharging machining. The state of the discharging gap is complex and variable. There are many factors which have effects on the state. Furthermore, practical application wants rapid measurement to meet the satisfaction of pulse response. Normal measurement method is not suitable to obtain the information of the micro gap. The paper introduces an important relationship between the voltage of discharging pulse and the size of discharging gap. Then, several typical measurement methods and their interrelated basic circuits are presented, such as gap average voltage measurement method, gap peak voltage measurement method and electrical discharging sensing method, etc. The measurement circuits are designed correspondingly. Pulse response test under different conditions are carried out. Results show that the measurement circuits can detect the variance of gap size respectively and rapidly. The measurement methods are effective.