Abstract: Aiming at on-line diagnosis problem about valve leakage in petrochemical enterprises, a simulation test platform of preset defect gates valve leakage is established. By the application of acoustic emission (AE) technology testing means combined with Fluent software simulation of flow field under leakage state, the distribution of AE characteristic parameters are studied in the process of internal leakage. Results show that as the pressure increases, the leakage rate in valve will increase, and the AE signal characteristic parameters (including energy, amplitude, ASL, RMS, etc) will also change regularly. The larger the size of the defect is, the more obvious the change trend shall be. RMS-leakage rate curve is fitting with least squares, and the formula is put forward on quantitative diagnosis for valve leakage.