The invention relates to the technical field of disinfectants, in particular to a low-temperature disinfectant and a preparation method thereof. The low-temperature disinfectant is prepared from components in percentage by mass as follows: 0.1%-1% of polyhexamethylene biguanide, 0.05%-0.1% of composite quaternary ammonium salt, 25%-35% of a synergist, 15%-25% of an anti-freezing agent, 0.1%-1.5% of a pH regulator and the balance of deionized water. The preparation method comprises the following steps: adding the deionized water, the polyhexamethylene biguanide and the synergist into a beaker, uniformly stirring and mixing the mixture, respectively adding the compound quaternary ammonium salt and the anti-freezing agent, stirring and dissolving the components, adding the pH regulator, and regulating the pH value of the mixed solution to 7.5-8.0 to prepare the low-temperature disinfectant. The low-temperature disinfectant is suitable for being used in a low-temperature environment at the lowest temperature of -30 DEG C, wherein the sterilization rate can reach 99.99% after acting on the surface of an object for 10 minutes, and a layer of sterilization protective film is formed on the surface of the object after 45 minutes, and the sterilization time is as long as 15 days. By means of the product, the labor cost and the sterilizing agent cost are saved, and the environmental influence caused by excessive spraying of the disinfectant is completely avoided.