This study explores the relationship between perceived social support and non-suicidal self-injury (NSSI) among adults, along with the mediating role of negative emotions and loneliness. From July to September 2024, a questionnaire survey was conducted among 1 751 adults in Nantong. The results showed that the prevalence rates among adults were 5.08% for NSSI, 5.88% for stress, 8.00% for anxiety, 6.74% for depression, and 7.76% for loneliness. The perceived social support score was 64.09 ± 8.72, indicating a relatively high level. Mediation analysis revealed that both negative emotions and loneliness play mediating roles between perceived social support and NSSI. The results indicate that high levels of perceived social support can directly reduce the occurrence of NSSI in adults and also indirectly decrease its occurrence by alleviating individual negative emotions and loneliness.