As an emergency, food insecurity threatens people's well-being, while social capital is expected to enhance their resilience in this situation. This study examined the relationship between food insecurity and social capital during the COVID-19 lockdowns in Shanghai. We collected a dataset of 1064 participants by random sampling. Structural equation modelling was used to analyse the dynamics of social capital before and after lockdowns. The results show that the level of post-lockdown social capital was higher than that of pre-lockdown social capital. Pre-lockdown social capital predicted the extent to which people suffered from food insecurity and their approaches to obtaining food. Participation in group purchases and food exchange with other residents predicted the levels of post-lockdown social capital. The results shed light on the interaction between emergencies and social capital. Our study theoretically contributes to understanding social capital through a dynamic perspective.