Abstract: A kind of green solvent, ionic liquid, was introduced as an extracting agent, and a new method of dispersive liquid-liquid microextraction based on ultrasonic-assisted in situ ionic liquid formation (DLLM-UAISLF) was established for the High Performance Liquid Chromatography (HPLC) determination of atrazine in water. Five mL of water was treated using 80 μL of HMimCl as the extracting agent, 400 μL of LiNTf₂ as the ion-exchange material, ultrasound time of 10 minutes and centrifuge time of 8 minutes at 4000 r/min. During this process, the droplets of ionic liquid HMimNTf₂ were formed in water and the precipitates were then separated for determination of atrazine by HPLC. The detection limit of atrazine is 0.01 mg/L and the detection values range from 0.01 to 0.5 mg/L. The proposed method yielded recoveries of 100.4%-106.7%, which are obviously better than those ( < 67%) of direct liquid-liquid microextraction. This method has potential in the determination of organic pollutants.