The outbreak of COVID-19 has forced Chinese international education to move online. An emerging number of studies have been published on online teaching and learning during the pandemic, few of which, however, focus on international students in China. This study examined the predictive effects of an online learning environment and student engagement on international students’ learning of Chinese as a foreign language (CFL). Self-reported data were collected in an online questionnaire survey involving 447 international CFL students at eight universities located in different geographical regions in China. Descriptive statistics revealed the participants’ favorable perceptions of an online learning environment, student engagement and Chinese learning achievement. The results of multiple linear regression revealed that three online learning environment factors, i.e., course accessibility, student interaction, course organization, and student engagement exerted significant positive effects on Chinese learning achievement. The implications of the study are discussed for the sustainable enhancement of the online learning environment to improve international students’ online language learning.