The reactive azo dye Procion Red MX-5B (PR MX-5B) is hard to degrade completely in aqueous solutions with traditional biochemical methods. Electron beam irradiation was carried out to investigate the degradation at concentrations varying between 100 and 500 mg/L. Some influence factors such as absorbed does, initial concentration pH value and different system on degradation efficiency are discussed. The degradation is found to follow first-order kinetics by high performance liquid chromatography (HPLC) with UV/V is detection. The results indicate that the factors do have effect on the reaction,for example, the degradation rates follow an order of ·OH oxidative system with saturated oxygen >·OH oxidative system with saturated air > e−aq reactive system with saturatednitrogen and isopropyl alcohol. Hydroxyl radical attacked azo linkage and aromatic ringof PR MX-5B leading to the fracture of benzene ring formed a series of byproducts aniline and small molecules organic acid. Electron beam irradiation is an effective and promisingmethod in waste water treated.