This paper attempts to show causes of border conflict between Thailand and Cambodia, and to look for the means of solving the conflict. Preah Vihear Temple is an old Khmer temple ruins situated on the border of Thailand and Cambodia. UNESCO decided to list it as a World Heritage Site on July 7, 2008. However, the two countries have been in a state of border conflict since that time. The conflict leaves dozens of casualties. This paper shows that there are two causes of conflict. The first one is the method named "political reform by judicial power", which has been used for Thailand's political conflict. The other is the difference of border line on two maps that are used in Thailand and Cambodia. Based on these two causes, this paper examines the possible solutions for the border conflict.