Abstract: Lake Hulun is the largest lake in northern China, and the quality of the water environment has an important influence on the ecological environment adjustment of this area. To solve the problem that the total phosphorus content in Lake Hulun exceeds the standard level in the recent years, we collected various water samples from Lake Hulun in spring, summer, autumn and winter. Through the relationship with the monthly monitoring data of the lake section of rivers for many years, we analyzed the spatial-temporal distribution, occurrence characteristics, the source of pollution and the influencing factors of Lake Hulun. The research results show that: (1) The concentration of total phosphorus (TP) in Hulun water was 0.145-0.301 mg/L in autumn, 0.090-0.360 mg/L in winter, 0.104-0.434 mg/L in spring and 0.049-0.219 mg/L in summer, and all were in the range of V grade of Environmental Quality Standards for Surface Water (GB 3838-2002). The spatial distribution of TP was obviously different between different seasons. The concentration of TP in the water around the lake was higher than that in the center of the lake in winter, the opposite was true in autumn. and it was higher in the lake estuary of the Kherlen River in spring and summer. (2) The phosphorus concentration in winter was much difference from that in the other three seasons, and dissolved phosphorus was the main form of TP in winter. The content of ρ(DTP) was 76.2% of ρ(TP). However, TP was mainly in particular form in spring, summer and autumn, and ρ(PP) in three seasons was 55.1%, 64.1% and 58.9%, respectively. (3) The characteristics of three rivers into Lake Hulun indicated that the ρ(TP) in the Kherlen River > ρ(TP) in the Hulungou River > ρ(TP) in the Wulshun River. In conclusion, the main impact factors which affect the total phosphorus concentration are the variation of water volume, frozen, rivers into the lake and sediment suspension.