To understand the responding mechanism of phosphorus concentration to external nutrient reduction in large shallow lakes, phosphorus concentrations, capacity in water column, and seasonal variations in Lake Taihu were calculated, based on 14 years (2005-2018) monthly monitoring data undertaken by Taihu Laboratory for Lake Ecosystem Research, Chinese Academy of Sciences. The responses of phosphorus capacity to water level, water volume and cyanobacterial bloom condition had been discussed. The result showed that total phosphorus concentration in Lake Taihu has not decreased significantly after the tremendous catchment restoration activities in the past 14 years. Fluctuations of total phosphorus concentration among seasonal timescale were spatially larger than inter-annual differences. The average total phosphorus concentration was 0.113 mg/L (n=1788), based on statistics of 32 sites in the lake and 3 layers in water column monitoring in the past 14 years. The average particulate phosphorus concentration was 0.077 mg/L, which was the main fraction of total phosphorus in the water column of Lake Taihu. Dissolved total phosphorus concentration was 0.036 mg/L in average, and the soluble reactive phosphorus concentration was 0.015 mg/L, which occupied only 13% of total phosphorus in water. The capacity of total phosphorus in Lake Taihu ranged between 410 t and 1098 t, with an average value of 688 t. The average capacities in spring, summer, autumn and winter were 604, 792, 673 and 683 t, respectively. Total phosphorus capacity in summer was much higher than that in other seasons. Conditions of algal blooms and hydrology, such as chlorophyll-a concentrations, suspended solid contents and water level, significantly influenced the spatial and temporal dynamics of phosphorus capacities in Lake Taihu. Influence of algal biomass dynamics on phosphorus capacity was even greater than hydrological conditions. The results suggested that the fluctuation of phosphorus concentrations in Lake Taihu was influenced by algal bloom and macrophyte dynamics under changing climate change scenarios. The restoration target of total phosphorus concentrations of 0.05 mg/L in the end of 2020 was difficult to achieve shortly. To further decrease the total phosphorus concentration in Lake Taihu, drastic decrease of external phosphorus loading and large-scale restoration of macrophyte vegetation are needed. For the phosphorus target management, more attention should be paid on the discharge reduction and inflow phosphorus loading, and the fluctuation of phosphorus concentration impacted by the future uncertainty of climate change favorably considered.