In China, social workers face great at-work stress, job burnout and turnover. Determining how to prevent and alleviate their job burnout and improve their work enthusiasm and engagement has become urgent. Using the affective events theory and challenge stressor-hindrance stressor framework, this study explored the impacts of different types of stressors on job engagement and its associated mechanisms and then examined the protective roles of positive emotion and career resilience. A total of 430 social workers in Beijing were investigated. The unique and combined contribution of the stress components to job engagement has been examined. The results showed that both challenge stressors and hindrance stressors had significantly negative impacts on social workers’ work engagement and positive emotion, and positive emotion had a significant positive influence on work engagement. Positive emotion fully mediated the negative relationship between challenge stressors and work engagement, and partially mediated the negative relationship between hindrance stressors and work engagement. Furthermore, career resilience can buffer the negative influence of challenge stressors on positive emotion.