Efficacy tests on Tetranychus cinnbarinus of Calathea makoyana for 5% pyrethrin in concentrations of 800 folds，1 000 folds，1 200 folds and 1 500 folds were studied.The results showed that best effect，which was over 90%，appeared with concentrations of 800 folds to 1 000 folds，however the results on 3 d and 5 d were declined comparing with 1 d after application，and the effect dropped drastically，which was not up to 80% on 7 d.Therefore，an interval of 7 d was suggested in practice.