On the early morning of the May 24th, Thai troops declared a unilateral military curfew and carried out the media censorship, without the approval from the caretaker government. Moreover, the troops surrounded the Red Shirts demonstrators in Bangkok, calling for a halt on the rallies. Since the "June Revolution" in 1932, 20 military coups have been brought out in Thailand, a signal for frequent army interventions into its politics. In other words, Thai military forces have played an important role in its national political life. Whenever the Thai constitutional institution malfunctions, military coups, as a political regulator, can be regarded as a significant method to break the deadlocks. This report aims to carry out an analysis on the changing political roles of Thai troops in the military coups during the development course of its constitutional institution, so that the reader can obtain a better understanding of the future political situation and development in Thailand.