With rapid development of the Internet and social media platforms,hundreds of millions of users have created and shared information as a large quantities of text,image,audio,and video data.Given this large volume of heterogeneous,multi-source,and complex social multimedia content,the challenge of providing effective content understanding and knowledge representation to users with more efficient and high-quality service has become the key to realizing the value of big social media data.This paper reviews research on social multimedia content analysis,knowledge extraction and representation,and on user modeling applications in recent years.In addition,research on social multi-modal feature fusion,cross-modal knowledge extraction and representation,and user modeling based on social media has been presented in detail.We then discuss development trends in social multimedia content knowledge representation,and review research into and application of user modeling.Finally,we summarize likely research directions for multimedia knowledge representation and user modeling.