Lake Chenghai is a plateau-enclosed deep lake located in Yongsheng County, Lijiang City, Yunnan Province, China. To understand the temporal-spatial distribution of euphotic depth and its influencing factors, we carried out field investigations including nine sampling sites in the lake from March 2016 to February 2017. The results showed that the mean value of the attenuation coefficient of photosynthetically active radiation and the euphotic depth were 1.06±0.25 m^-1 and 4.64±1.27 m, respectively. There were no significant difference in the spatial distribution of the euphotic depth in the whole year, months, rainy and dry seasons. Meanwhile, the euphotic depth were significantly different among months (throughout the whole year, as well as in the rainy and dry seasons), and the highest and the lowest monthly value of euphotic depth were 6.49±1.03 m (May) and 3.63±0.48 m (July), respectively. Moreover, the phytoplankton biomass was the main regulating factor that controlling the euphotic depth, and the impact of suspended solids on euphotic depth was found in rainy season, few impact of chromophoric dissolved organic matter on euphotic depth was detected. To further test the indirect influencing factors that affecting euphotic depth, the Spearman correlation between the phytoplankton biomass and its ecological factors was also conducted. This study could accumulate the limnological data and provide the reference for the environmental protection of Lake Chenghai.