Abstract: p-nitrobenzoic acid, a kind of aromatic nitro compound for the two substituents on the contrapositions, can not be dissolved in water but can be dissolved in organic solvent. In order to obtain the photodegradation behavior change of p-nitrobenzoic acid, radiation induced degradations of p-nitrobenzoic acid at 266 nm laser light and at 254 nm ultraviolet radiation were studied by laser photolysis technology and UV at room temperature in different conditions. The absorption spectra and degradation efficiencies were investigated. From the laser photolysis transient spectrum, it is found that an excitation state appears at 310 nm. Compared the UV degradation with UV/H₂O₂ degradation experiments, it is found that UV/H₂O₂ degradation is more effective than the other method. The addition of H₂O₂ plays an important role in the degradation of p-nitrobenzoic acid.