The invention discloses a caprolactam crystal purifying method. The caprolactam crystal purifying method comprises the following steps: subjecting amide oil obtained during a process of liquid-phase rearrangement or liquid-phase solvent rearrangement or gas-phase rearrangement of cyclohexanoneoxime to ammonium sulfate removal, and performing caprolactam cooling crystallization, recrystallization and crystal treatment, crystallization mother liquor posttreatment and other processes to obtain a high-purity caprolactam solid product, a high-purity nylon slice product and a high-purity caprolactamliquid product. With the caprolactam crystal purifying method, integrated technologies of cooling crystallization, evaporative distillation separation, extractive separation and the like are adoptedto replace or partially replace benzene extraction, water back extraction, ion exchange, hydrogenation and other processes in original technologies, the wastewater discharge is reduced, the flow pathis short, the energy consumption is reduced, and the caprolactam solid product with relatively high quality can be produced.