To explore the effects and mechanisms between chronic pain and depression in middle-aged and older adults in China, and to provide reference for promoting pain management and improving interventions.

13,253 middle-aged and older adults from the fifth issue of the China Health and Retirement Longitudinal Study (CHARLS) were included. Propensity score matching method, logit model, OLS regression and Bootstrap mediation test were used to explain the mediating effects of subjective life expectancy (SLE), sleep duration and Internet use between chronic pain and depression and the moderating role of social participation.

The overall effect size of chronic pain on depression was 0.876 (95%CI=0.781-0.972), with a direct effect of 0.745 (95%CI=0.668-0.822), accounting for 85.05%, and an indirect effect of 0.131 (95%CI=0.094-0.169), accounting for 14.95%. The mediating effects of SLE, sleep duration, and Internet use were 0.087 (95%CI=0.071-0.103), 0.093 (95%CI=0.066-0.121), and -0.049 (95%CI=-0.085--0.013), representing 9.93%, 10.62%, and -5.60% of the total effect respectively. Social participation negatively moderated the relationship between chronic pain and depression（β=-0.095，95%CI=-0.186--0.004）.

Chronic pain not only directly exacerbates depression in middle-aged and older adults but also indirectly worsens depression through SLE and sleep duration. However, Internet use and social participation can have compensatory and alleviating effects. It is recommended that physical and psychological therapies be emphasized and applied simultaneously, with special attention given to key populations such as women, rural dwellers, and chronic patients. Additionally, “Internet plus healthcare” and grassroots communities should be utilized to enhance pain management and intervention for middle-aged and older adults.