[Objectives] To study the toxic effect and antiviral activity of anthraquinone extract ofPolygonum cuspidatumon infection of Koi herpes virus(KHV). [Methods] The MTT method and CPE microscopy were used to detect the common carp brain(CCB) cytotoxicity of the P. cuspidatumanthraquinone extract in 48 h. Eight groups of different concentrations of theP. cuspidatumanthraquinone extract 1. 96, 3. 91,7. 28, 15. 63, 31. 25, 62. 5, 125, 250 μg/mL experimental groups and a control group without drug effect were set up. After determining the maximum non-toxic range of theP. cuspidatumanthraquinone extract, the viral replication inhibition test was carried out. [Results] The concentration of the P. cuspidatumanthraquinone extract 31. 25 μg/mL was recognized as the maximum non-toxic concentration. The survival rate of CCB cells was higher than 80%, and the toxic dose(CC50) of the drug for 50% cell death was(72. 67 ±2. 12) μg/mL. The maximum inhibition rate of theP. cuspidatumanthraquinone extract was 78. 63% ± 5. 47% at a concentration of 31. 25 μg/mL, and the 50% effective drug dose(IC50) for inhibiting the virus was(13. 67 ±0. 47) μg/mL, and the therapeutic index(TI) was 5. 48 ± 0. 49. In the direct virus killing test, the highest virus inhibition rate was 32. 21%. [Conclusions] Under the experimental conditions, it can be concluded that the P. cuspidatumanthraquinone extract has high anti-KHV activity, and at the same time. It is expected to lay a theoretical foundation for the research ofP. cuspidatumanthraquinone extract against KHV.