Abstract: The 50% thiamethoxam flowable concentrates for seed coating were prepared and their effect on the controlling of cotton aphid were increased. To construct the formulation, a series of wetting agent, dispersing agent, film-forming agent, thickening agent and other agents were screened and optimized by wet milling method and recurrent selection method. The wet milling method was ultimately chosen as the optimal method to prepare the 50% thiamethoxam flowable concentrates for seed coating which contains the following fomula: thiamethoxam 50% as active ingredient; FD 3% and BC-10 1% as wetting agent; SP-2836 2.5% and SK-24 2.5% as dispersing agent; veegum 1% and xanthan gum 0.05% as thickening agent and BF 308 2.5% as film-forming agent. Its quality index and effect on the germination potential and the germination rate of seeds were determined. The results showed that the above formulation had excellent morphology, high suspension rate, perfect heat storage stability, and its effect on the germination potential and germination rate of cotton was discrepant with that of the blank control. The further field experiment revealed that, when effective dose was 187.5 g/hm2, the 50% thiamethoxam flowable concentrates for seed coating had an excellent control effect on cotton aphids in the 4-and 5-leaf stage of cotton, and the control effect was 83.94% and 53.94%, respectively. These results demonstrated applying the concentrates in the field was feasible.