Abstract: The joint-toxicity of the insecitide mixture of lambda-cyhalothrin and triazophos in Conopomorpha sinensis Bradley were studied by leaf immersion method .CTC of this mixture was equal to 183.2~255.0 in a significantly synergism.According to the maximum of the proper proportion of triazophos to lambda-cyhalothrin ,a 21% EC synergistic formulation was manufactured .Field control efficiency of 21% EC against Conopomorpha sinensis Bradley was excellent.The mixture,applied at 168~210mg/kg the tip effect was 81.65%~86.87%,and the population effect was 85.05%~88.11%,which were equivalent to 2.5% EW lambda-cyhalothrin and significant super to 40% EC triazophos.