Abstract: To find a highly effective and low-toxic disinfectant on Vibrio parahaemolyticus, twenty-two kinds of disinfectants including commonly used benzalkonium bromide and polyhexamethylene guanidine hydrochloride (PHMG) in the field of aquaculture and medicine were used for evaluating the killing ability on Vibrio parahaemolyticus. The results showed that the germicidal efficacy of PHMG had the best germicidal efficacy among 22 disinfectants against V. parahaemolyticus. The results indicated that 100% of V. parahaemolyticus was killed when the PHMG concentration reached 0.2 mg/L. The killing effects for 7 common pathogens and 1 probiotic (Bacillus coagulans) indicated that PHMG had high efficacy in killing Vibrio, modest ability in killing Streptococcus iniae etc., and the worst killing efficacy on B. coagulans. The acute toxicity test showed that the LC₅₀ of PHMG was 80.28 mg/L at 24h and 23.32 mg/L at 48h, and the safety concentration (SC) was 0.59 mg/L. The protective test of PHMG for L. vannamei infected by V. parahaemolyticus showed that the survival rate of L. vannamei was (77.78±5.01)% when the PHMG reached 0.5 mg/L, and there was no significant difference with the other three high-density groups. With the increase of PHMG concentration, the number of V. parahaemolyticus in hepatopancreas decreased significantly, and the number of V. parahaemolyticus in 1.1 mg/L and 1.4 mg/L groups decreased to 0 after 48h. The results of the PHMG degradation test showed that 0.5 mg/L PHMG slightly decreased on the 5th and 6th days, and 1 mg/L PHMG was generally stable during the experiment of the 7d. This study demonstrated that PHMG has the characteristics of high efficiency, low toxicity and low degradation, and is an ideal disinfectant for preventing L. vannamei AHPNS infected by V. parahaemolyticus.