Abstract: In order to provide theoretical foundation of Vibrio control for Fenneropenaeus merguiensis, pathogenicity of Vibrio parahaemolyticus to Fenneropenaeus merguiensis by different quantities, and under different temperatures, salinities, pH, and concentrations of nitrate nitrogen, nitrite nitrogen, ammonia nitrogen were studied. The results showed that the death rate of Fenneropenaeus merguiensis was 100% in 24 h when the quantity of Vibrio parahaemolyticus was beyond 3.92×10⁶ CFU, and the death rate was 50% when the quantity of Vibrio prehaemolyticus was 3.92×10⁵ CFU. When the temperature was 32℃, the accumulation death rate was the highest, and the death rate increased with the increase of temperature within a certain range. When the temperature was (24±1)℃, the death rate was the highest when salinity was 10‰, followed by 30‰, and it was the lowest when salinity was 20‰. When the temperature was (24±1)℃ and the salinity was (22±1)‰, the death rate was the highest when pH 9, and it decreased when pH 7, and it was the lowest when pH 8. When the temperature was (24±1)℃ and the salinity was (22±1)‰, the death rate was the highest when the concentration of nitrate nitrogen was 30.0 mg/L, followed by 20.0 mg/L, and it was the lowest when the concentration of nitrate nitrogen was 10.0 mg/L. Under the same temperature and salinity, the death rate was the highest when the concentration of nitrite nitrogen was 10.0 mg/L, followed by 5.0 mg/L, and it was the lowest when the concentration of nitrite nitrogen was 1.0 mg/L. The death rate was the highest when the concentration of ammonia nitrogen was 1.5 mg/L, followed by 1.0 mg/L, and it was the lowest when the concentration of ammonia nitrogen was 0.5 mg/L. The research indicated that when the quantity of Vibrio parahaemolyticus was up to 3.92×10⁵ CFU or 3.92×10⁴ CFU for 72 h, it was hard to control. The death rate of Fenneropenaeus merguiensis would rise with the increase of temperature when the temperature was from 26℃ to 32℃. The influence of salinity and pH to the pathogenicity for Fenneropenaeus merguiensis might be related to bacteriophage. The results indicated that nitrate nitrogen had stress effect on Fenneropenaeus merguiensis. In a certain range, pathogenicity of Vibrio parahaemolyticus to Fenneropenaeus merguiensis was more serious and the death ratio was higher with the increase concentration of nitrite nitrogen (1.0~10.0 mg/L) and ammonia nitrogen (0.5~1.5 mg/L). The results lay a foundation for the Vibrio prevention of Fenneropenaeus merguiensis.