The invention relates to a 4,6-dyhydroxy pyrimidine reaction system tail gas treatment process, and belongs to the technical field of chemical product recycling. The process comprises the steps that firstly, tail gas is conveyed into a condenser, gaseous formaldehyde is converted into liquid formaldehyde through low-temperature condensation to be collected, and the tail gas obtained after the formaldehyde is removed is conveyed into a stabilization tank and subjected to stabilization introducing pressure maintaining; the rear end of the stabilization tank is sequentially connected with two stages of falling film absorbers, each falling film absorber is connected with an absorption liquid circulating tank for providing absorption liquid, the absorption liquid circulating tanks absorb ammonia in the tail gas, and then the tail gas enters an incinerator to be incinerated. In the whole technological process, equipment is simple, operation is easy and convenient, no high-temperature high-pressure equipment exists, the safety coefficient is high, the formaldehyde and ammonium hydroxide can be recycled in the tail gas treatment process, formaldehyde in production raw materials is supplemented, and the ammonium hydroxide can be sold as chemical materials; in the tail gas treatment process, the work environment is improved, and atmospheric pollution is relieved.