The invention discloses a preparation method of a Cu/ZnO catalyst for preparing methanol from synthesis gas, which relates to a method for preparing a catalyst. The method comprises the following steps: mixing Cu2+ with Zn2+ in a nitrate, then complexing the obtained mixture and a polyhydroxy organic acid so as to obtain a collosol, and drying the collosol so as to obtain a xerogel, wherein in a reducing atmosphere formed by NH4NO3 (formed by NO3.H2O for adjusting the pH value and NO3-) and polyhydroxy organic acid in the process of combustion in an inert atmosphere, the Cu2+ is reduced into monoatomic Cu, but the Zn2+ is not reduced in the process of combustion and exists in the form of ZnO. The Cu/ZnO catalyst prepared by using the method provided by the invention can directly be applied to the reaction of preparing the methanol from the synthesis gas without a reductive passivation process, and has a good catalytic activity. The method disclosed by the invention has the advantages of mild reaction condition, low equipment cost and high catalytic performance and the like, and is simple to operate.