Disclosed is a water quality toxicity detection method based on fish activity analysis. The method comprises the following steps that 1, crucian is adopted as a biological monitoring object so as to be subjected to real-time monitoring; 2, a target crucian contour is extracted through conversion from RGB to HSV color space, crucian groups are monitored in real time, and a crucian tracking video sequence is obtained; 3, crucian motion data analysis and detection are performed, wherein 3.1, differences among the crucian velocity speed, a counter area and an area mean value are adopted as main characteristic data; 3.2, a mature detection model is generated on the basis of a Naive Bayes classifier algorithm; 3.3, novel characteristic data is adopted for detecting and judging whether the detection model is mature or not; 3.4, real-time water quality data is detected in an online mode through the mature detection model, and finally online detection of the water quality toxicity is achieved. Online real-time detection can be achieved, sensitivity and continuity of water quality detection can be improved, the detection cost can be lowered, and real-time effective detection can be performed on a large number of unknown water quality toxicity conditions.