The main objective of many studies in the physical, behavioral, social, and biological sciences is the elucidation of cause-effect relationships among variables or events. Many causality problems, occur when new words and behaviors are mapped from individuals to the Internet or are created by the Internetitself. Causality is hidden behind correlations; conclusion made by correlation analysis is likely to be unreliable or even wrong; and in absence of causality, methods based on correlation is unable to intervene, control and manage. Thus, causal analysis is necessary in social media. This paper first introduces the value, importance, and necessity of causality analysis, followed by causality problems existing in social media. Then, a brief overview of the recent research on causal inference is provided with analysis basic theory, problems and research status. Finally, comparisons among previous studies are made to suggest the future research directions and causality application in social media