Utilizing a sample of 286 community-dwelling adults with severe mental disorders (SMDs) in Beijing, this study examined their social and community participation during COVID-19 pandemic. The descriptive results showed that adults with SMDs living in the pandemic Beijing mostly engaged in social activities, followed by productive and leisure/recreational activities. More than two-thirds of the participants indicated that their participation was not sufficient. The multivariate analyses revealed that higher social support and self-esteem predicted more participation days, higher social support and independent usage of Health Kit were linked to more participation items, while higher social support and stronger self-stigma were associated with lower perceived participation sufficiency. Thus, community mental health professionals need to provide more tailored interventions to people with SMDs to enhance their participation performance and perceived participation sufficiency during the pandemic era.