Abstract: Valve is an essential fluid control device in industrial production, and the inner leakage of valve is hard to detect and judge. In recent years, the Acoustic Emission (AE) technique has been widely used in valve leakage detection because of its high sensitivity. Due to being easily influenced by the noise and fluid flow condition, the application of the traditional AE parameter "RMS" (acoustic emission root mean square voltage) in valve leakage evaluation is limited. A new AE parameter AErms (average acoustic emission energy) for valve leakage evaluation is proposed in this paper. Through experiments of gas-valve leakage, the leakage evaluation results by AErms and RMS is compared. The result shows that the new parameter AErms has higher resolution, and the estimation error of inner leakage flow rate is less than 10%, which can meet the engineering application requirements.