The invention relates to a method for preparing a pyridino- triazolone compound (II) through flow chemistry. The method comprises the following steps: a hydrazide compound (I) is dissolved in an organic solvent, the solution is placed in a first storage tank, an oxidantis dissolved in the organic solvent, and the solution is placed in a second storage tank; and aterials in the first storage tank and the second storage tank are conveyed through metering pumps respectively and enter a mixer to be mixed, reaction liquid obtained through mixing continuously enters a tubular reactor to be subjected to oxidation rearrangement reaction, the temperature of oxidation rearrangement is 0-70 DEG C, the retention time of the mixed reaction liquid in the tubular reactor is 0.1-10 h, material liquid obtained after reaction enters a receiving tank and is subjected to post-treatment, and after-treatment is conducted on the material liquid to obtain the product (II). In the tubular reaction, the material back mixing is less, the mass transfer and heat transfer efficiency is high, and the side reaction is obviously reduced; a reaction system is simple, raw materials, especially hydrazide compounds, are easily obtained, a substrate does not need to be prepared in multiple steps, and the total yield is relatively high; and the continuous tubular reaction can accurately control reaction parameters and has an automation prospect;.