The assessment of antioxidant activity in vitro is an important area in functional food research. However, there were many problems, such as the confusing specification of antioxidant capacity and the improper application of antioxidant activity assessment assays, which hampered the comparison and selection of antioxidant functional foods greatly. Thus, development of a validated method for antioxidant activity assessment is a worldwide problem. In this study, the characteristics and shortcomings of the antioxidant activity assessment methods (the chemical and cellular assays) were discussed in terms of inducing method, reaction mechanisms, and result indicators. In addition, the development prospects of the antioxidant activity assessment methods were proposed.