This paper examines prefectural judges' legal knowledge during the Ming dynasty. Specifically, it studies the judges' preparation of legal knowledge prior to taking their offices and the avenues and mechanisms by which those judges obtained legal knowledge in their offices. Looking at the prefectural judges as a particular group, this work emphasizes the significant role the ″institution″ played in the judges' acquisition of legal knowledge. By way of tracing the official career experience of the Ming prefectural judges, this paper studies the mechanisms of judge selection, local judicial review (xiangyan) system, and the impact of gradual institutionalization of ″transferring to the offices of supervising secretaries and censors″(tuizhixingqu) at the central government after the mid-Ming on the prefectural judges' legal knowledge. Although the prefectural judges were special judicial officials at the local government offices, there were no special considerations and requirements for their legal credentials and expertise in the process of their recruitment and appointment. In other words, the selection system of the prefectural judges in the Ming did not provide effective mechanism to encourage candidates to master the legal knowledge before they took office. Nevertheless, while this system was not ideal, it did not lead to chaos in local judicial system, which, in large part, could be attributed to the strict local judicial review system. The judicial review system of the Ming required that prefectural judges were only authorized to judge cases involving beating with the light stick|any judgments of cases involving the penalties of beating with the heavy stick or above should be reported to superior offices for review, a procedure known as ″shenxiang.″ The officials at the provincial surveillance commissions and the regional inspectors were more equipped with special legal knowledge, and thus were in charge of the review. The judicial review system not only reduced the chances of judicial errors made by the young judges who lacked legal knowledge in adjudication, but, more importantly, provided important channels in the exchange of opinions through which the judges could gain actual legal knowledge. Meanwhile, the system of ″transferring to the offices of supervising secretaries and censors″ that became institutionalized after the mid-Ming created chances for the young prefectural judges who performed quality work to take important surveillance offices at the capital. Indeed, both the emphasis on the legal capacity during the process of ″transferring″ and the examination on their legal knowledge after the judges arrived at their new offices at the capital provided the judges with motivation mechanisms in obtaining and spreading legal knowledge.  In existing researches, scholars claimed that due to the fact that the judicial officials in the Ming dynasty - such as the prefectural judges - did not prepare themselves well in gaining sufficient legal knowledge prior to taking office, generally speaking, the officials in late imperial China did not possess adequate legal knowledge. In addition, scholars also asserted that the bureaucratic mechanism in the Ming and Qing periods was not capable of developing professional legal knowledge among officials, because there was no actual requirement for practical legal knowledge in the civil service examinations. Based on the study of the legal knowledge among the prefectural judges during the Ming, this paper illustrates that imperial officials took various paths in obtaining legal knowledge, and different official groups could develop different types of legal qualities at various levels. Therefore, the study of the legal knowledge of imperial officials should be more specific and careful. Likewise, the civil service examination was not the sole mechanism that affected the acquisition of legal knowledge by officials and other systems also existed. While the prefectural judges failed to obtain sufficient legal knowledge prior to taking office, they had received considerable on-the-job training. Motivated by the practice of ″transferring to the offices of supervising secretaries and censors,″ a large number of officials eventually became recognized censors who had equipped themselves with professional legal knowledge. Therefore, when we study what legal knowledge the late imperial officials acquired and what role institutions had played in ensuring the acquisition, we should pay more attention to their dynamics and processes.