Mental fatigue, first known as brain fag, is one of the common clinical fatigue types. Due to the increase of the intensity and proportion of mental work, mental fatigue has an increasing prevalence among the people working in all fields especially, especially in the military field. In recent years, mental fatigue has become an important part of fatiguerelative research. How to prevent, control and alleviate mental fatigue is an important issue, which is based on evaluating or determining the degree of mental fatigue. Because mental fatigue has strong subjectivity and its mechanism is still unclear, there are many evaluation methods, but with no unified standard. This article reviews the evaluation methods of mental fatigue, including symptomatic, psychobehavioral, and physiological and biochemical assessment, and discusses the main contents and principles of various evaluation methods, so as to provide reference to mental fatigue research.