Background <p>Life-space mobility (LSM) is a critical health indicator in older adults, the mechanisms underlying the relationship between subjective cognitive decline (SCD) and LSM remain unclear.</p> Aims <p>This study examined depression as a mediator between SCD and LSM, and assessed whether perceived social support (PSS) moderates the relationship between SCD and depression among Chinese community-dwelling older adults.</p> Methods <p>We seek to elucidate psychosocial mechanisms of the SCD-LSM link and inform targeted intervention strategies. Drawing on a face-to-face interview sample of 287 community-dwelling aged, this cross-sectional study utilised a moderated mediation analysis. Key constructs were evaluated by the Subjective Cognitive Decline Questionnaire-9, 15-item geriatric depression scale, Perceived Social Support Scale, the Life Space Assessment, respectively.</p> Results <p>The results showed that SCD was negatively associated with LSM (β = -0.213, <i>p</i> &lt; 0.001). Mediation analysis indicated an indirect association between SCD and LSM through depression (indirect effect = -1.868, 95% CI [-2.825, -1.029]), accounting for 41.6% of the total association. Furthermore, PSS was identified as a significant moderator in the relationship between SCD and depression (β = -0.088, <i>p</i> &lt; 0.05), with a stronger association observed among older adults with lower PSS levels. The interaction term contributed a unique incremental variance of ΔR² = 0.0086 to the model.</p> Discussion <p>Establishing a social support system holds promise for improving life-space mobility and alleviating depression among community-dwelling older adults with subjective cognitive decline, thereby enhancing their well-being.</p> Conclusion <p>A negative association between SCD and LSM was observed, with depression partially mediating this relationship. Importantly, PSS demonstrated a statistically significant moderating effect on the relationship between SCD and depression, although the effect size was small.</p>