The invention relates to a treatment solution for hydrazine waste liquid, and the treatment solution comprises the following main components: 0.1-20% of hydrogen peroxide, 0.01-1.0% of potassium sorbate, 0.1-20% of acetic acid, 0.1-10% of phosphoric acid, 0.01-1% of sodium selenate, and the balance of water. The treatment solution is prepared by the following steps: adding water with a volume being about half of the liquid volume of the treatment solution to be prepared into a container, starting a stirring device, adding hydrogen peroxide, potassium sorbate, acetic acid, phosphoric acid, andsodium selenate sequentially, and adding water to achieve a volume to be prepared after all the solid materials are added; continuing to stir for 30 min and stopping; allowing the solution to stand for 1 h, filtering to remove residues and insoluble substances so as to obtain a clear solution which is the treatment solution.