As a powerful tool to analyze and explain organizational behavior, organizational legitimacy is increasingly becoming the hot topic of organization theory researchers. Up to date, the study of organizational legitimacy has been carried out mainly through three approaches: institutional, strategic and evaluator approaches. The evaluator approach is the most recent one in organizational legitimacy field, and its core concept is legitimacy judgement which means the evaluator’s self-judgement of the legitimacy about a given organization. This paper states the definition of legitimacy judgment, analyzes its judgement models, evaluative perspectives and psychological process, and the application value of legitimacy judgment theory. It has also pointed out eventually research prospects for legitimacy judgment theory.