To improve the thermal safety and synthetic efficiency during the synthesis process of 3-Nitro-1，2，4-triazol-5-one （NTO） by conventional methods， a continuous flow reaction system was designed and prepared based on the solid contents and kinetics at different reaction stages of nitration. The continuous flow synthesis of NTO was realized by combining microfluidic reaction technology with tubular reaction technology， using 2，4-dihydro-1，2，4-triazol-5-one （TO） and 85% nitric acid as the main raw materials. The reaction conditions and continuous flow system were optimized. NTO with a purity of 99.53% and a yield of 81.4% was achieved at a reaction temperature of 45 ℃， a nitration residence time of 9 min， a molar ratio of n（TO）∶n（HNO₃） equals 1∶6. The chemical structure of NTO synthesized by the continuous flow method was characterized by ¹H and ¹³C NMR， element analysis （EA）， infrared spectroscopy （FT-IR）. In addition， the crystal form， particle morphology， thermal stability and mechanical sensitivity were characterized by the powder X-ray diffraction （XRD）， thermal analyzer （DSC-TG）， optical microscope and BAM technology. The results show that NTO grows into stable β-form. At the heating rate of 10 ℃·min^-1， the thermal decomposition peak temperature is 276.23 ℃ and the mass loss rate during thermal decomposition is 85.12%. The impact sensitivity is over 40 J， and the friction sensitivity is over 360 N. Compared with NTO synthesized by the flask method， the thermal decomposition peak temperature is increased by 2.95 ℃， and the mass loss rate is elevated by 4.44%. The mechanical sensitivities is similar， the crystal morphology is regular and the particle size distribution range is narrowed. The continuous flow synthesis time is 90% shorter than that of the flask process， with 3.4% higher of the yiel， and the preparation efficiency and safety are improved.