The purpose of this paper is to study underground Mark Six, which is among the most popular activities in Taiwan. Although it involves complicated financial transaction and lots of people, the deriving debt has no legal status according to principle ¡§the gamble debt is illegal¡¨ proscribed in Taiwanese civil law. This thesis focuses on how this system operates without the assurance of the legal system, which is widely believed as the foundation of modern property right. This Data were collected by in-depth interview and participant observation, including 23 interviewers in three main roles and other related actors, gamblers, brokers, bankers, and then, observing the transaction details of underground Mark Six in the illegal casino to analyze the issue specifically. This study identities three major mechanisms that maintain the operation of underground Mark Six: social Network, violence and risk Management. First, the definition of Social network is the relationship construction under the illegal Mark Six transaction. Trust and reputation, derived from the social network, protect transaction safety as a normative force. Next, the mechanism of violence is the transaction progress which judges in underworld way. Also, the mechanism of violence has the technique of evasion of law. Third, the mechanism of risk management is by different layers' actors to work on, and therefore, these actors cause the variation of transaction rule, method and restriction. In order to avoid debt quarrel, for instance, gamblers in lower layer usually decrease the risks by separating the creditor's right to different uplinks.For the brokers in the middle layer, they use a specific transaction record to insure the transaction execution. What's more is that the bankers in the top layer would control the signed Mark Six number for some specific number to prevent a horrible ¡§Hot Pack¡¨ result. I also find that recently Underground Mark Six is toward network technology, gathering with the traditional manual operation. These two executions so called ¡§Computer Operation¡¨ and ¡§Paper Operation.¡¨ Computer operation, moreover, is toward to be an institutionalization franchise, leading the Underground Mark Six to a technology operation, especially for account and managing risk.