Abstract: The synergistic toxicity of spirotetramat mixed with thiamethoxam to Bemisia tabaci were measured by insecticide-impregnated filter method,and the results showed that the co-toxicity coefficient(CTC)ranged from122.97 to 167.43,showing the synergistic effect.Based on the result above,40% mixtures of spirotetramat and thiamethoxam SC were made,and its toxicity and control efficacy on B.tabaci and its safety to ornamental chrysanthemum cultivars were studied.The results showed when the active ingredient was 90 g a.i.·hm-2,which was the recommended dose,double dose 180 g a.i.·hm-2,and quadruple dose 360 g a.i.·hm-2,respectively.The mixtures of spirotetramat and thiamethoxam had no significant impact on the growth of three ornamental chrysanthemum cultivars,Calendula officinalis and Callistephus chinensis and Tagetes erecta.So the compound was safe to ornamental chrysanthemum cultivars. After spraying,the control effects of 40% mixtures of spirotetramat and thiamethoxam SC with under 60-90 g a.i.·hm-2 treatment could reach 75.60%-90.67%,which was higher than that of mixtures of 22.4% spirotetramate SC and 25% thiamethoxam WG treatments.Therefore the mixtures were proved to have available and persistent control effect against Bemisia tabaci.