This study examined the affordances of an online learning platform used in a Chinese university for online teaching and learning during the pandemic period. A usefulness theoretical perspective was adopted to examine three types of affordances of the platform, namely, educational affordances, social affordances, and technological affordances. Both quantitative and qualitative data were collected and analyzed, including survey questionnaires, observation, and semi-structured interviews. A range of educational affordances emerged from the results, including Representation, Resource sharing, Community-building, Promoting interaction, and Administration. However, despite the respondents' perceived ease of use of the platform, results indicate that the platform played a limited role in increasing learners' social presence. A framework for examining usefulness has been developed based on the results. Pedagogical implications are proposed and suggestions for future research are provided.