China's aging is deepening and the number of chronic diseases among the elderly is increasing. By exploring the influencing factors of depressive symptoms as well as the mediating effects of the degree of somatic pain and the length of sleep between the number of chronic diseases among the elderly and their depressive symptoms, we provide theoretical references for improving the mental health of the elderly. Relevant data of 6,826 chronically ill older adults aged ≧60 years in 2020 newly released by China Healthy Aging and Tracking (CHARLS) were selected and statistically analyzed by using chi-square test, multivariate logistic regression analysis, and model 6 of the Spearman and PROCESS programs. The results showed that gender, age, place of residence, marital status, alcohol consumption status and degree of normal work and labor, the number of chronic diseases, sleep duration, and the degree of somatic pain are factors that affect the likelihood of depressive symptoms among older adults with chronic diseases, and the degree of somatic pain and sleep duration have a chain-mediated effect on the number of chronic disease co-morbidities and depressive symptoms among older adults, as well as an independent mediating utility. Emphasizing the impact of multiple chronic diseases on the occurrence of depressive symptoms, it is recommended that more attention be paid to the management of somatic pain in older adults, early prevention and treatment of somatic pain, maintenance of good moods, appropriate exercise, increased leisure and recreational activities, and increased sleep duration to reduce the occurrence of depressive symptoms in older adults with chronic disease co-morbidities and improve the quality of healthy life in older adults.