In order to obtain the characteristics of seasonal stratification of Lake Tianchi of Tianshan Mountains, an alpine deep lake, continuous monitoring on vertical dynamics of hydrochemical parameters (water temperature, conductivity, dissolved oxygen (DO) , pH,chlorophyll-a) and algae cell density were conducted from June to October 2014. Lake Tianchi had a short-term of thermal stratification(from June to September). The depth of thermocline ranged from 2 m to 18 m in summer, however, it moved down continuously as the time progressed in autumn, and was below 18 m in October; The hydrochemical parameters and algae cell density showed significant seasonal stratification caused by thermal stratification, especially to the distribution of DO and chlorophyll-a in summer, which had a significant impact on water quality. Besides, from June to October, the concentration of DO decreased gradually, with>8mg/L in the epilimnion(0-10 m) and about 4 mg/L in the hypolimnion (deeper than 18 m) in September. As a result, seasonal hypoxia caused nutrients in the sediment moving upward and made water quality worse. Hence, it is necessary to strengthen water quality monitoring in Lake Tianchi to prevent the algal bloom in summer and fall; Chlorophyll-a and algae both increased firstly and then decreased along with depths. However, concentration of chlorophyll-a was higher in the depth of 2-12 m than the water surface, and algae cell density was higher in the depth of 5-15 m, indicating that the depth of 5-15 m was suitable for algae growth. Meanwhile, the vertical change of conductivity and pH value also illustrated the algae growth, which may provide theoretical support for the sampling and analysis of eutrophication in Lake Tianchi.