The outbreak of COVID-19 has changed the mobility, accessibility, and behaviors of tourists dramatically. Under the impact of COVID-19, tourists’ perception of crowding and emotions in tourism destinations are expected to change due to the uncertainty of health risks associated with visitors’ behaviors. This study conducted an onsite visitor survey at Leiqiong Global Geological Park, a highly visited nature-based tourism destination in Hainan Province, China, and aims to 1) examine tourists’ perceptions of crowding and emotions by applying the normative theory of crowding, and 2) identify factors associated with tourists’ perceived crowding and emotions. Study results identify the thresholds of perceived crowding and positive emotions based on the indicator of people per view (PPV) and indicate that mask-wearing can reduce perceived crowding and enhance tourists’ positive emotions. Results also suggest that the level of crowding and COVID-19 prevention strategies and implementation can affect tourists’ emotions in nature-based tourism destinations.