Abstract: Through theoretical analysis, the functional relationship between volumetric leaking rate of gas and root meansquare of acoustic emission (AERMS) during internal leakage of valve is established. In addition, acoustic featuresof ball valve in case of ○-ring damages and under specific leaking rates are investigated. Energy analyses is made forinternal leakage signals by using signal analyzing and processing methods based on theory related to wavelet packet. Theresults show that in case of singular damage in ○-ring, energy is distributed predominantly within 12.5~62.5 kHz withacoustic emission signal AERMS in double logarithmic relationship with internal leakage rate of gas volume in ball valve.Consequently, acoustic emission theory can be used to identify internal leakage of valve along gas pipeline and to determinevolumetric leakage rate.