Abstract: Eugenol has been shown to mitigate the stress response in crayfish (Procambarus clarkii) during out-of-water conditions. This study further investigate the anesthetic effects of eugenol on crayfish to provide a theoretical basis for the precise application. Crayfish of two size groups—large (22.06±2.46) g and small (10.32±1.73) g—were selected. Four treatment groups with different eugenol concentrations and one clean water control group were established, with three replicates per group and five shrimp per replicate. Eugenol was mixed with ethanol at a volume ratio of 1:3, and anesthesia was administered via both immersion and spraying methods. Morphological parameters including body weight and body length were measured for each experimental shrimp. The coefficient of determination and path coefficients were calculated in relation to the corresponding complete anesthesia time and recovery time. After significance analysis, non-significant variables were removed, and a multiple linear regression equation was established. The hepatopancreas and gill tissues of the shrimp tested at the optimal anesthetic concentration of 0, 1, 3, 6, 12 and 24h under spraying conditions were observed histomorphically. Results indicated that the optimal anesthetic concentration for large-sized individuals was 7.5 g/L under both immersion and spray methods, yielding complete anesthesia times of (8.01±1.96)min and (5.32±2.30)min, respectively, and recovery times of (25.18±5.49)min and (31.74±7.45)min, respectively. For small-sized crayfish, the optimal concentration was 5.0 g/L, with complete anesthesia times of (4.99±1.37)min and (4.70±1.72)min, and recovery times of (21.81±6.19)min and (25.12±9.49)min, respectively. Path analysis and regression modeling revealed that morphological traits, such as body weight, body length, and body width, significantly influence the anesthetic response. Histological observations demonstrated that large-sized crayfish exhibited earlier signs of hepatopancreatic vacuolation and gill epithelial rupture than smaller individuals under optimal anesthetic conditions. This study explored the anesthetic effect of eugenol-ethanol mixture on crayfish, clarified the influence of body size parameters on complete anesthesia and recovery time, constructed a regression model, and observed the changes in the tissue structure of gill and hepatopancreas at the optimal concentration, providing theoretical support for the formulation of precise anesthesia plans and ensuring the safety of aquaculture.