Lakes across the Qinghai-Tibetan Plateau (TP) have undergone substantial environmental changes in recent decades, under the influence of climate warming and enhanced precipitation. But the long-term changes in lake optical properties and their responses to climate change on the TP remain less explored. This study utilizes Landsat series datasets from 1986 to 2024 to estimate a fundamental lake optical property—the Secchi disk depth (Z_SD) in TP lakes, for tracking the long-term shifts in TP lake ecosystems. To accommodate the limited spectral information of Landsat 5/TM imagery, an improved semi-analytical QAARGB model was proposed to enhance the applicability of the semi-analytical model on lakes with relatively low Z_SD (< 1 m). To maintain the consistency of Z_SD retrieval across Landsat series datasets, MODIS data were also employed for cross-calibration. The results unveil a noteworthy upward trend of Z_SD across TP lakes over the nearly 40 years (with average Sen’s slope of 0.019 m/yr, P < 0.05), with more pronounced improvements observed in the western and central TP regions. Analysis of long-term lake Z_SD and meteorological factors revealed three distinct response patterns of lake Z_SD to climate change on the TP. These patterns were predominantly associated with NDVI (33.0% of lakes), lake area (31.0%), and air temperature (4.9%), unveiling clear spatial heterogeneity in the dominant meteorological factors associated with interannual Z_SD variations. These findings highlight the cascading impacts of climate change on TP lakes—mediated by hydrological expansion, watershed vegetation, and thermal regime—ultimately reshaping their optical and ecological characteristics.