This paper reports on the trajectory of college students' emotions as they engaged in online learning during a pandemic and how their emotions related to their learning. Through a qualitative analysis of 11 college students' reflections and interview data collected over one semester in a university in China, the case study shows the complexity of students' emotions in the aforementioned context. The students' emotions demonstrated a dynamic transition from anxiety and curiosity to emotional stability, and then back to anxiety, a phenomenon that interacted with the changing sources in the research context. The students also felt that their emotions while engaging in online learning interacted with their learning. Implications of the study include caring about and promoting students' social-emotional well-being and encouraging students to regulate their emotions while learning online during a pandemic as well as in normal times.