Abstract: Imidacloprid 10% wetable powder, cypermethrin 10% emulsifiable concentrate and chlorpyrifos 48% emulsifiable concentrate were compared for their ability to control aphids and thrips on alfalfa; their application safety and environment effects including residual effects were also assessed. Gas chromatography was used to assess chemical residue levels. At 1-7 days after treatment, the efficacy of imidacloprid, cypermethrin and chlorpyrifos against alfalfa aphids at application rates of 35.7 g a.i./ha (available ingredient/hectare), 75.0 g a.i./ha and 480.0 g a.i./ha were 80.83%-94.78%, 79.29%-87.80% and 90.93%-98.90%, respectively; against thrips efficacy were 78.33%-95.57%, 78.56%-91.67% and 92.78%-100.00%, respectively. The half-life of imidacloprid, cypermethrin and chlorpyrifos were 4.78, 3.69 and 2.48 days, respectively. Seven days after application residues of imidacloprid and chlorpyrifos in alfalfa were less than 0.5 mg/kg while cypermethrin residues did not drop below 0.5 mg/kg until 14 days after application. Based on the pesticide residue standards of the China and Codex Alimentarius Commission (CAC), the maximum residue limit (MRL) of imidacloprid, chlorpyrifos and cypermethrin were recommended at 0.5, 1.0 and 0.5 mg/kg, and the recommended safe application interval 7, 14 and 7 days respectively, in alfalfa.