There are advantages of quick response and simple measurement in the water biological toxicity detection method based on the photosynthetic inhibition effect of algae. However, more than ten photosynthetic fluorescence parameters are derived from the PSⅡ photosynthetic reaction center, showing poor sensitivity or no response to typical PSⅠ photosynthetic inhibitors. In this paper, based on the characteristic that toxic stress will cause deformation of algae fluorescence kinetics curve, and the change degree is proportional to the toxicity intensity, the morphology of the multiphase chlorophyll fluorescence kinetics curve is directly taken as the analysis object. Based on the accurate location of the characteristic sites, a comprehensive characterization parameter CPI based on the segmentation inhibition of the curve is constructed. The toxicity response time, response sensitivity and stability were compared with the commonly used photosynthetic fluorescence parameters Fv/Fm and the comprehensive fluorescence parameter PIabs. The results showed that for paraquat, a typical PSⅠ inhibitor, the comprehensive parameter CPI showed significant inhibition at 15 min (1 mg·L-1 and above), while Fv/Fm had no response. Compared with PIabs and Fv/Fm, the minimum detection limit and relative standard deviation decreased by 70.3% and 24.1% and 75.6% and 30.0%, respectively, under 8h stable inhibition. Atrazine, a PSⅡ inhibitor, showed significant inhibition in the whole concentration range of samples within 15 min, and the minimum detection limit and relative standard deviation decreased by 52.4% and 51.6% and 75.6% and 30.0%, compared with PIabs and Fv/Fm. These conclusions indicate that the comprehensive parameter PICTE, as a response index, can be used to detect the biotoxicity of PSⅠ and PSⅡ inhibitors, and it shows good response sensitivity and stability. The results of this study provide an important parameter for highly sensitive and high-precision detection of biotoxicity in water based on algae photosynthetic inhibition.