Abstract: Phenol and xylene degradation by hydrodynamic cavitation were studied using Multi-orifice plates as the generating device of hydrodynamic cavitation. Resultsobtained from experiments show that the phenol degradation rate is 39.1% when its concentration is 30 ~ 40mg/L and the xylene degradation rate increases up to 55.35% when its concentration is 3.0 ~ 3.6mg/L. Acidic condition is more conducive to their degradation than neutral and alkaline conditions. With long hydraulic cycle time, the amount of phenol and xylene degradation tends to increase.