3,4-thiadiazol-2-one with 1,4-dibromobutane which was then demethylated then intramolecular alkylated. 5-Methoxy-3H-1, 3, 4-thiadiazol-2-one was synthesized by three steps with CS2, CH3OH and KOH as raw materials.The structures of the compounds were characterized by 1H NMR and 13CNMR spectra. The crystal structure of target compound was determined by X-ray single crystal diffraction. Target compound belongs to the triclinic, space group P1, with a =7.8400(16) ? b =10.464(2) ? c =10.514(2) ? α=63.84(3)? β=79.62(3)? γ=89.42(3)? V =759.2(3) ?, Z =4, wR(F2) =0.125, μ=0.37mm-1。