Testamentary capacity is one of the civil competences, it means that a natural person enjoys the capacity or qualification to establish testament and deal with his property. Recently, the cases of testamentary capacity assessment of the mentally disordered are increasing. This article firstly introduces the concepts of the testament as well as the testamentary capacity, and then summarizes the assessment standard of the testamentary capacity, by using the Banks v. Goodfellow case as a basis to make the standard criteria including: the understanding of the nature of a will and codicil, the knowledge of the general extent of one's assets, the knowledge of the natural object of one's bounty, the understanding of the impact of the distribution of the assets of the estate, and the absence of a delusion specifically affecting the distribution of the estate. The impact factors of the testamentary capacity, including dementia, mood disorder, schizophrenia, alcohol, drug, and undue influence, etc., are summarized. Lastly, the related assessment tools such as the Mini-Mental State Examination, the Clock-Drawing Test, and the Testament Definition Scale are introduced briefly.