In order to study the effects of six traditional Chinese medicines，such as Nepeta cataria L.,Potentilla chinensis Ser.,Humulus lupulus Linn.,Potentilla discolor Bge.,Stemona japonica(Blume) Miq.and Ｒeynoutria japonica Houtt.,against porcine reproductive and respiratory syndrome in vitro,the Marc 145 cell model was established in this experiment.Based on the study of their maximum safe mass con centration on Marc-145 cells,combined with the observation of cell morphology and MTT method,the three actions of blocking,inhibiting and inactivating the virus were determined,respectively.The results showed that the maximum safe mass concentrations of Nepeta cataria L.,Potentilla chinensis Ser.,Humu lus lupulus Linn.,Potentilla discolor Bge.,Stemona japonica(Blume) Miq.and Ｒeynoutria japonica Houtt.on Marc-145 cells were 0.25 mg/mL，1.25 mg/mL，0.63 mg/mL，0.31 mg/mL，1.56 mg/mL， and 0.47 mg/mL.In the experiment of anti-PＲＲSV effect in vitro，it was found from the cell morphology observation that under the three modes of action on PＲＲSV，the cells treated by Potentilla chinensis Ser.and Ｒeynoutria japonica Houtt. had no obvious lesions，and the treatment of other four drugs showed dif ferent degrees of lesions.From the inhibition rate of PＲＲSV，the highest inhibition rates of blocking，inhi bition and direct inactivation of Nepeta cataria L.were 80.6%，52.2% and 56.5%,respectively.The highest inhibition rates of PＲＲSV by three modes of action of Potentilla chinensis Ser.were 115.8%,93.0% and 125.4%,respectively.The highest inhibition rates of PＲＲSV in the three modes of action of Humulus lupulus Linn.were 61.5%，32.0% and 82.4%，respectively.The highest inhibition rates of PＲＲSV in the three modes of action of Potentilla discolor Bge.were 15.6%,129.4% and 57.7%,re spectively.The highest inhibition rates of PＲＲSV in the three modes of action of Stemona japonica (Blume) Miq. were 120.2%，61.8% and 71.9%,respectively.The highest inhibition rates of PＲＲSV in the three modes of action of Ｒeynoutria japonica Houtt.were 110.4%，94.3% and 130.8%,respective ly.Combined with morphological observation and inhibition rate results，Potentilla chinensis Ser.and Ｒey noutria japonica Houtt.had the best anti-PＲＲSV effect，followed by Nepeta cataria L.and Stemona japon ica(Blume) Miq．