In the present study, the in vitro inhibitory activity of extracts from radix isatidis on neuraminidase (NA) was investigated by the chemical fluoremetic determination to establish the quality control method for antivirus action of radix isatidis. The initial study indicated that radix isatidis had obvious in vitro inhibitory activity on NA with IC50=(0.90±0.20) mg(herb)·mL-1. The correlation between logarithmic dose and reaction rate showed a “S” shape and a linear curve (linear equation, y＝8.725 9+1.216 9 log(D), R=0.999 2) when the reaction rate was converted to probit-quite similar to Tamiflu’s reaction curve, which hinted that radix isatidis had the same inhibitory function on NA as Tamiflu. According to the reaction type and the regularity of “parallel lines of qualitative effect”, the experimental condition was optimized and a statistic method was confirmed based on the principle of bioassay statistic. Then the bioassay method for antivirus potency of radix isatidis based on fluorometric determination was established. The results of bio-potency assay showed the qualitative differences of radix isatidis samples sensitively and quantitatively. Meanwhile, this method has good reproducibility with RSD=5.78% and reliability. The quality bioassay control method based on chemical fluorometric determination can reflect the pharmaco-dynamic features of Chinese medicine herb.