As an important strategic resource, psychological capital has a positive impact on knowledge sharing. However, there are few studies on the relationship between them. Under the framework of job demand-resource model and social exchange, a new theory model is constructed and tested through multilevel linear analysis with the data collected from questionnaires. The results show that (1) collective psychological capital has a significant positive impact on individual work engagement and individual knowledge sharing; (2) collective psychological capital has a significant positive impact on collective trust, and collective trust mediates the relationship between collective psychological capital and individual knowledge sharing; (3) collective trust positively moderates the relationship between individual work engagement and individual knowledge sharing.