One important aspect of the regional autonomy of Dai nationality is the autonomy in using the written language. For over half a century, this autonomy has seen some success but also some setbacks. It went through two main periods: the first was from 1953 when a local representative meeting in Xishuangbanna Autonomous Region decided to create the new Dai written language from the traditional written language, promoting the new script in education and newspapers. The second period spans from 1986 until today. In 1986, the people's congress of the prefecture adopted the Decision of Using the Traditional Dai Written Language. Since then, all circles, including education, media, etc, were devoted to popularising the traditional Dai written language, but the effort seems unsuccessful. On the basis of fieldwork and documentary review, this article makes a preliminary investigation into the legal system with regard to the autonomy of using the written language in Xishuangbanna.