Politeness, as a linguistic phenomenon, pervades almost all the civilized social-cultures and languages, which works as a sort of softening agent to smoothen the course of communication. As people from different cultures may view differently on what politeness is and how to be polite, misunderstandings may arise if cultural differences are neglected in cross-cultural communication. This thesis is intended to make a comparative study of cultural differences in politeness between English and Chinese,first from the disparity in their conceptions of politeness,and then proceeds to discuss the underlying psychological factor. Lastly,based on the awareness of these cultural differences and the knowledge of the cause of the differences, this paper proposes some applicable advice to achieve successful cross-cultural communication.