<p>To explore the association between comprehensive living environment and depression trajectories and examine the potential mediating role of sleep duration. This study included 7,773 middle-aged and older participants based on the China Health and Retirement Longitudinal Study. Living environment was assessed using outdoor PM_2.5 level, solid fuel use, water type, room type and room temperature. Depression trajectories were identified using Latent Class Trajectory Model. Multinomial logistic regression and mediation analysis was used for analysis. Three depression trajectories were identified: low-rising (63.99%), moderate-rising (29.36%), and high-rising (6.65%). Poorer living environment was associated with moderate-rising depression trajectory (OR = 1.06, 95%CI: 1.02–1.10) and high-rising depression trajectory (OR = 1.20, 95%CI: 1.11–1.30). These associations were particularly strong at high risk levels of living environment exposure, with ORs of 1.30 (95%CI: 1.09–1.55) and 1.58 (95% CI: 1.10–2.28) for the respective trajectory. Sleep duration positively mediated the association between living environment and high-rising depression trajectory, with a mediation proportion of 7.32%. Poorer living environment is associated with higher level of depression trajectories. Furthermore, sleep duration partially mediates the relationship between living environment and the high-rising depression trajectory. These findings highlight the importance of improving living conditions and sleep as potential strategies to mitigate depression risk in this population.</p>