With the rapid expansion of higher education in China, education-occupation mismatch has become a critical issue in the labor market. In regard to the current education-occupation mismatch, 24% of college graduates experienced vertical mismatch between the degree level and the occupation, and 34% underwent horizontal mismatch between the field of study and the occupation. With respect to the cause for education-occupation mismatch, the college ranking and the academic performance significantly affected vertical mismatch, with the higher-ranked college and the better academic performance reducing the risk of vertical mismatch; the field of study and the professional certifications mainly affected horizontal mismatch: the fields with stronger occupational specificity and higher linkage with the labor market were less likely to lead to horizontal mismatch, and obtaining professional certifications helped reduce horizontal mismatch. As to the consequence of education-occupation mismatch, it brought about significant wage penalty in the first job. These findings broaden the research perspectives and theoretical explanations of education-occupation mismatch, and reveal the role of education-occupation mismatch in social stratification, which has been overlooked before.