In higher education, the pathways through which teacher expectations could contribute to students’ academic achievement are an area of limited empirical investigation. In this study, we investigated the mediating role of the socioemotional classroom environment in the relations between university teachers’ early expectations and their students’ later achievement. The participants were 176 teachers and their 6,506 first-year undergraduate students from public universities in China. Data from teachers’ initial expectations, students’ prior and year-end achievement on standardized tests, and students’ perceptions of socioemotional factors within the classroom were collected. As students were nested in classes, multilevel structural equation modeling was employed for data analysis. The results showed that, at the individual level, with students’ prior achievement controlled, the extent of the teacher’s differential treatment, the quality of the teacher-student relationships, and the quality of the peer relationships in turn were statistically significantly related to the university teachers’ initial expectations, which ultimately was associated with the individual students’ year-end academic achievement. Further, the university teachers’ expectations for their individual students played a role in the quality of the peer relationships which subsequently contributed to students’ later academic achievements. Moreover, the university classes whose teachers tended on average to have higher expectations tended to achieve at higher levels. However, we did not identify mediating paths via socioemotional factors from university teacher expectations to student achievement at the class level.