This dissertation aims to analyze and constitute the theory of knowledge in Xunzi. In other words, the author tries to present a concealed theory of knowledge in Xunzi using the contextual analysis of the meanings and content of Xunzi’s words and the theory-building method that focuses on basic philosophical questions. Therefore, this dissertation is organized according to the major theses listed as follows: the capabilities of subjects, the qualities of objects, the moral standards of knowledge and justifications, the categories and essence of knowledge, and morality and knowledge. The process of human cognition can be classified into two parts, which are the capabilities of subjects and the qualities of objects. The author suggests that Xunzi utilizes sensibility, perception, memory, the abilities of realizing and projecting tonglei (統類), and the choice of values as the capabilities of subject. Comparatively, the qualities of objects are recognized when subjects perceive objects. Further, objects have two forms: concrete and abstract objects. Qualities of the finite being are concrete object. The rules of nature and the rules of human society are abstract objects. According to Xunzi, as names are imitations of objects, names belong to abstract object as well. However, beliefs are not always in line with facts. Knowledge is generated only when beliefs are consistent with facts. Xunzi indicates that one’s belief originating from perception, illusion, and name-substance relationship may deviate from the fact. Thus, a method used to justify the belief is necessary. He argues that the belief-fact consistency can only appear under the hsü-yi-ching（虛壹而靜）situation because the impediment of knowing no longer exists. This article treats hsü-yi-ching as an ethical standard of knowledge. In addition, Xunzi argues that the following two methods can be used to examine whether a belief-fact gap exists. The first one is pien-ho and fu-yen（辨合、符驗）. The second one is feasibility. More precisely, a match of beliefs and facts appears when “those who sit and talk can prove that their speech is doable”（坐而言之，起而可設張而可施行）. The author deems these two methods as the “justification of knowledge.” In addition, we can classify knowledge appears in the book of Xunzi. First classification is made on the basis of origins, which comprises sensation, study, projection and practice. If we classify knowledge on the basis of the content, skills, aesthetic perception, morality and conception could be included in the second classification. The possibility and essence of knowledge are major issues of epistemology. Since Xunzi is not skeptic about epistemology, there should be a intermediary between subjects and objects. And “Name”（名）is assumed as the intermediary by Xunzi. In other words, “Name” makes it possible for understanding. In addition, Xunzi considers that the correspondence between judgment and facts is the essence of knowledge, so the author indicates it belongs to truth as correspondence. However, the discussion of knowledge does not take knowledge qua knowledge in Xunzi. In Xunzi’s view, knowing is to correctly practice moral motives using knowledge. Through analyzing Xunzi, the author would like to present that ethical judgment is nothing more than the choice of values. Ethical practices in three aspects are discussed. These are the subjective conditions of ethical practices, the objective conditions of ethical practices, and the principles of ethical choices. Firstly, subjective conditions mean that human beings acquire ethical knowledge by learning and making ethical judgments by informed deliberation(lü慮). Secondly, Wise-King(Sheng-Wang聖王) had enacted the rules of ethical actions. Although these rules may be revised and modified as time evolves, it remains unchanged principle throughout different periods of time. Finally, the principles of ethical judgment are the following: mutual takes priority over private benefits. The harmony between the rules of proprity(li禮) and moral emotion is the best ethical choice. In brief, through analyzing Xunzi, the author constitutes the theory of knowledge that consists four elements. These are the process of cognation, the moral standards and justifications of knowledge, the possibility and essence of knowledge, and the choice and practice of morality.