The purpose of this research is to explore the determining factors about the drug trafficking defendant pleaded guilty by the game theory point, when the defendant face to the investigations. Participants of the research are 204 drug trafficking defendants in Taiwan prison. The experimental method including the questionnaires and face to face interview to clarify the most important factor about the drug trafficking defendant pleaded guilty on court. This paper presents a theoretical analysis of the 2009 amendments to Taiwan's Drug Prevention and Control Ordinance, which effected the drug trafficking defendant pleaded guilty and behavior patterns .The findings revealed the most important factor that the drug defendants willing to plead guilty is due to reduce a penalty . In addition, the provisions about over a certain number of the drug possession increasing the penalties will also change the behavior patterns of drug trafficking. Based on the findings, some implications are also proposed to be help to those drug-trafficking crime and law-related amendments.