Abstract: To study the fully automated synthesis method of the hypoxic imaging agent ¹⁸F-nitroimidazole(¹⁸F-FMISO) and analyze the factors affecting the radiochemical stability of ¹⁸F-FMISO, ¹⁸F^- produced by the cyclotron was transferred to the Sumitomo CFN-MPS200 synthesizer, captured by the QMA column and rinsed into the reactor, dried twice to remove water, and then dissolved with acetonitrile 10 mg 1-(2’-nitrate-1’-imidazolyl)-2-oxo-tetrahydrofuran-3-oxo-tosyl-propanediol(NITTP) undergoed a nucleophilic substitution reaction. The reaction solution was hydrolyzed with hydrochloric acid and then neutralized with buffer solution, and then entered a preparative high-performance liquid phase for separation. The mobile phase was 15% acetonitrile in water, the flow rate was 3 mL/min, and the retention time was 11 min. The solvent was removed with a rotary evaporator, and then dissolved with physiological saline to add a stabilizer to obtain ¹⁸F-FMISO injection. The effect of different specific activities, stabilizers, and rotary evaporation temperature on the radiochemical stability of the product was studied. The result shows that the EOS is (45±5)%（n=20）.The synthesis time is 50 min, and the sodium ascorbate is used as a stabilizer. The radiochemical purity of the product is 95% after 6 h, and ascorbic acid and ethanol can not be used at temperatures above 50 ℃ as a stabilizer. ¹⁸F-FMISO can be fully automated with the CFN-MPS200 synthesizer. The product yield is high and the process is stable. ¹⁸F-FMISO is stable in weak alkaline solutions, which provides clinical convenience for hypoxic imaging of tumors.