The residual chlorine (RC) discharged from coastal power plant may have adverse effects on the phytoplankton in the surrounding waters, affecting the balance of the ecological system. To help us understand the inhibition mechanism of RC on phytoplankton, the RC discharged from the cooling water of a liquefied natural gas (LNG) project was simulated under laboratory conditions. The experimental subject was Chlorella sp. The experimental concentrations of RC were 0, 0.02, 0.05, 0.10 mg/L and 0.20 mg/L, based on the engineer's estimates of RC density in discharges. The simulation was conducted at 27℃, which imitated summer temperature. The testing times were 0, 24, 48, 72 h and 96 h. Results showed that at 27℃, the RC at high concentration (0.20 mg/L) had the greatest inhibitive effect on the growth of Chlorella sp., with the strongest retarding effect (25.95%) after 48h. The inhibition effect on Chlorella sp. by the highest concentration of RC remained constant after 48h. At a low concentration (0.02 mg/L), the RC promoted the activity of Chlorella sp., which is in accordance with the hormesis mechanism. At 0.05 mg/L and 0.10 mg/L, the RC displayed an inhibitive effect at 24, 48 h and 72 h, and there were no marked inhibitive difference between these three time points. After 96h, there was no significant difference in the inhibitive effect of these two RC concentrations. Based on the algae growth rhythm, a growth model was fitted, finding a significant linear relationship between the control group (CG) and experimental groups (EG). The difference equation was calculated by subtracting the growth equation from the CG equation, creating the corresponding integral equation. Finally, the cumulative loss ratio (CLR) was calculated using the relative loss integral equation. At 0.05mg/l RC, CLR increased between 0 h and 72 h, with a maximum value was 8.73% at 72 h and 96 h. At 0.10 mg/l RC, the CLR was the same as at 0.05mg/L, apart from after 96h, when the 0.10mg/L CLR began to decrease. The CLR at 0.20mg/L RC was larger than the CLR of other concentrations at all time points. The CLR were 12.95%,27.07%, 41.29% and 55.59% at 24,48,72 h and 96 h, respectively. Using the RC dissipative model, the water region under investigation had an RC of 0.05mg/L. The algae theoretical loss value at 72h was calculated using the CLR and the concentration of RC at 0.05 mg/L, and then the 0.05mg/L maximum. Using the phytoplankton survey from the Shanghai LNG project in September 2009, cell abundance at high tide and low tide was high in coastal regions and low offshore. The average diversity index (H') of phytoplankton, mean evenness index and mean richness index were low, and the simple degree mean was high. This showed that phytoplankton distribution of individuals among species was non-uniform, the structure of the community was unstable, the ecological system was weak, and the environment might be polluted. The RC at 0.05mg/L and 0.10mg/L was 0.047 km² at the most, and the mean value of cell abundance was 3.67×10⁷ cells/m³. We conclude that phytoplankton theoretical relative loss was 1.965×1012 cells, owing to algae growth rates being inhibited by the RC density of 0.05 mg/L after 72h.