In order to better maintain friendly relations between countries, maintain national image and promote international cooperation, appropriate diplomatic discourse has become a very important factor. Politeness principle has become one of the most important principles. Based on the transcribed texts of routine press conferences of the Ministry of foreign affairs, this paper explores the contents of politeness principle and the translation strategy in diplomatic discourse from the perspective of politeness principle. The analysis of diplomatic discourse helps to understand politeness principle more deeply. On the contrary, politeness principle also provides indispensable guidance for the construction of more appropriate and effective diplomatic discourse.