To produce the radioligand 11C-flumazenil at very high quality and specific radioactivity for routinely clinical imaging , the procedures for its synthesis and purification were developed with domestic PET-CM-3H-IT-I synthesis module, and 11C-CH3I was used as methylation agent. 11C-CH3I was first synthesized by liquid phase reaction, the synthesis conditions of radiotracer 11C-flumazenil were studied ,which included the alkali strength, alkali equivalent, solvents, temperature and purification conditions for the product. The optimum conditions were that 11C-CH3I was bubbled through a reactor at room temperature , containing a DMF solution of 1 mg desmethylflumazenic precursor and 1 mg NaH, the reaction was conducted at 55 ℃ for 2 minutes. The reaction solution was first transferred to Semi-HPLC for purification, the mobile phase consisted of acetonitrile-acetic acid-water (30∶4∶66), the flow rate was 5.0 mL/min, then the crude product was purified by C-18 Solid-Extraction Purification(SEP), the product retained on SEP cartridge was eluted with 1 mL alcohol, the eluant was diluted with 6 mL sterile injection water, the dilute solution passed through sterile membrane to end-product. The radiochemical purity and specific radioactivity were measured by High Performance Liquid Chromatograph (HPLC) with the mobile phase of acetonitrile-acetic acid-water (30∶4∶66), and the column was ODS (250 mm×4.6 mm, 5 μm). The results showed that the total synthesis time was (26±2) minutes from 11C-CO2 to obtain 11C-flumazenil injection solution, the synthesis yield of 11C-flumazenil was (45±4)% (decay corrected, n=10), the radiochemical purity was over 99% at specific activity of 4.7 TBq/mmol, the radioactivity concentration was 370～550 MBq/mL. The injection solution was proved to be sterile and pyrogen free. The radiochemical yield was increased greatly by optimizing the reaction conditions ,11C-flumazenil was synthesized from 11C-CH3I with domestic C-11 synthesis module, the quality and quantity of 11C-flumazenil was confirmed to be suitable for clinic use.