Abstract: Nitrogen is one of the key elements controlling the growth and bloom formation of cyanobacteria. Conversely, cyanobacterial bloom also affects nitrogen concentration variation and form transformation. By collecting cyanobacteria, sediment and water samples from Zhushan Bay of Lake Taihu, indoor incubation experiments were set up as lake water only (A0), lake water with algae in light-proof culture (A1), sediment column without algae in light-proof culture (A2), sediment column with algae in light light-proof culture (A3), lake water with algae in light culture (A4) and sediment column with algae in light culture (A5) to investigate the process of nitrogen transformation during different periods of cyanobacterial growth and decay. The results showed that: (1) The growth of cyanobacteria would uptake a large amount of dissolved nitrogen in the water column, and finally the DTN concentration decreased by 46.4% and NO₃⁻-N concentration decreased by 61.7% in A4, and the DTN concentration decreased by 60.7% and NO₃⁻-N concentration decreased by 80.6% in A5. (2) The decay of cyanobacteria induced decrease of DO concentration and accelerated the nitrogen removal from the sediment. At the end of the experiment, there was basically no change in the NO₃⁻-N concentration in the A0 and A1, and the NO₃⁻-N concentration in the A2 and A3 was reduced by 40.8% and 56.6%, respectively. (3) The decay of cyanobacteria increased the DTN concentration in the form of NH₄⁺-N. Nitrogen removal was inhibited due to the inability to convert NH₄⁺-N to NO₃⁻-N as a result of low dissolved oxygen conditions during the experiments. This study inditates that the growth process of cyanobacteria reduces the substrate concentration for denitrification through the uptake of NO₃⁻-N in the water column, which may reduce the denitrification efficiency in the short term; In contrast, the decay of cyanobacterial blooms promotes denitrification in sediments, but the resulting low DO concentrations can impede nitrification, breaking the coupled nitrification-denitrification process in the short term. For shallow lakes, frequent wind and wave disturbances can put the water column in an anaerobic-oxygen depletion alternation process, which can strengthen the coupled nitrification-denitrification process. Therefore, although the growth of cyanobacterial blooms competes with denitrification for NO₃⁻-N and inhibit lake denitrification processes in the short term, cyanobacterial blooms may enhance nitrogen removal efficiency of lake from the perspective of the entire life cycle of cyanobacterial growth-decay.