The argument-based approach to validation, based on Toulmin’s argument model, is a validation framework which prioritizes the collection of different types of evidence, manifests the relationship between them and gauges the process of validation. This approach is composed of two arguments: interpretative argument and validity argument. As this approach has become increasingly influential, the author believes that it is important to introduce its procedures and characteristics. After comparing it with the unified concept of validity, it is pointed out that this approach conforms to the key principles of the unified concept of validity and makes it easy to be operationalized in practice. In the end, this article suggests some issues to be further examined and clarified in this approach, hoping to bring insights into validation practice in China.