Process for preparing cyanuric acid

The present invention belongs to the field of organic chemical intermediate preparing technology, and is especially preparation process of cyanuric acid. The preparation process includes three steps of preparation of coarse cyanuric acid product, hydrolysis and water washing. In the hydrolysis step, coarse cyanuric acid product, saturated hot steam and sulfuric acid are pumped to the first one of pipeline connected two reaction towers to react while controlling the flow rate of sulfuric acid, the concentration of sulfuric acid and the flow rate of the coarse cyanuric acid product, with the reaction product being cooled, water washed and separated to obtain cyanuric acid. The hydrolysis in performed continuously inside a tower at high temperature and high pressure in high reaction speed. Therefore, the present invention has the advantages of short reaction period, simple operation, controllable product quality and high production efficiency.