Abstract: Mediated Discourse Analysis was proposed by Professor R.Scollon，which draws upon the relevant fields such as speech act theory，interactional sociolinguistics，enthnography，and the new literacy studies.It aims at social actions and social problems，and focuses on mediated action，mediational means，practice，sites of engagement and the nexus of practice.This paper presents an overview of Mediated Discourse Analysis，mainly involves its theoretical background，basic concepts，theoretical disciplines，and research methods.Furthermore，it compares with Critical Discourse Analysis，and hence highlights the advantages and prospects of MDA.