Public health students have been seen as a potential force to meet the demand for health workers during the coronavirus disease 2019 (COVID-19) pandemic. However, few studies have provided empirical data. This study was conducted to summarize the experiences of public health students who engaged in voluntary service in response to the COVID-19 outbreak in Guangzhou, China. A cross-sectional study was conducted among postgraduate and undergraduate students at the School of Public Health, Guangdong Pharmaceutical University, in August 2021. A self-designed online questionnaire was used to collect data on the experience of voluntary service during the early stage of the outbreak (in February 2020) and during the normalization stage of the prevention and control of COVID-19 (in June 2021) in China. Among the 96 students, 40 (41.7%) participated in voluntary service in February 2020, and 56 (58.3%) participated in voluntary service in June 2021. Most of the students participated in the voluntary service due to the motivations to help others (55.2%), to apply theoretical knowledge to practice (74.0%), to improve their fieldwork skills (72.9%), and to gain the experience for future careers (80.2%). Most volunteers were driven by professional responsibility (81.3%). More than half (53.1%) of the students felt anxious during their voluntary service. A lower proportion of students felt anxious in June 2021 than in February 2020 (44.6% vs 65.0%, P = .049), while a higher proportion of students found voluntary service harder than expected in June 2021 than in February 2020 (33.9% vs 7.5%, P = .002). Most students improved their knowledge and skills about COVID-19 after the training, but some knowledge and skills still needed improvement after their voluntary service. Public health students could help support the health system during the COVID-19 pandemic by providing adequate training and protection. More efforts should be made to provide psychological support for student volunteers and to optimize the curriculum to bridge the gap in public health education between theoretical knowledge and practical skills in responding to public health emergencies.