This study examines the research methods, topics, and trends of empirical MOOC research to gain a comprehensive understanding of the MOOC phenomenon through reviewing 541 empirical MOOCs research published from 2009 to 2019. The results indicate that: (1) the majority of studies adopted quantitative research methods followed by mixed research methods and qualitative research methods, (2) the most frequently adopted data collection method was survey, followed by platform database and interviews, (3) almost half of the studies used at least two data collection methods such as survey and interview, (4) the majority of researchers adopted descriptive statistics for data analysis, followed by inferential statistics and content analysis, (5) the research topics primarily focused on students, followed by design-focused, context and impact-focused, and instructor-focused. Among these student-focused topics, learner retention, learning experience, social learning, and engagement were the most mentioned, and (6) the affiliations of the first authors of the MOOC studies were mainly from the U.S. followed by China and Spain. Implications and future research were discussed.