[Aim] To investigate the control effect of ethyl formate and methyl isothiocyanate mixture fumigation on the adults Acanthoscelides obtectus (Say) and the optimal formula for prevention and control.[Method] A jar airtight fumigation was used to screen optimum formula for A. obtectus control. Based on LC₅₀ values of ethyl formate and methyl isothiocyanate, the best combination was obtained using two factors quadratic regression rotation combination design and Lagrange multiplier method.[Result] There were significant differences in the toxicity of the two fumigants on the adults A. obtectus. The insecticidal effect of methyl isothiocyanate was stronger (LC₅₀ value was 0.667 mg·L^-1), followed by ethyl formate (LC₅₀value was 20.59 μL·L^-1). A quadratic polynomial was obtained by the two-factor quadratic regression rotation combination. Then, by the optimal target function and constraint function, we worked out the values of ethyl formate (102.702 μL) and methyl isothiocyanate (3.0263 mg) in the mixture.[Conclusion] When the ratio of ethyl formate to methyl isothiocyanate is 33.94:1, the best economic benefit and insecticidal effect can be obtained.