The definition of terms "nonconformity" in HAF003(1991), ISO9001:2000 and IAEA50-C-Q(1996) are compared and connotations are expatiated respectively. Management measures such as classifying, grading and leveling nonconformance (nonconformities) are introduced for the implementing of IAEA50-C-Q(96), and issues requiring more attention in the nonconformity management are proposed.