Abstract: A series of iron-molybdenum catalysts were prepared by controlling the acidity of ammonium molybdate solution in coprecipitation. The structure of the catalysts was characterized by N₂ adsorption-desorption, Raman, XRD, SEM and H₂-TPR. The Fe-Mo catalysts prepared with different pH values were investigated for their performance in methanol oxidation to formaldehyde reaction. The results showed that the acidity of ammonium molybdate solution affects the particle size, morphology, distribution and enrichment of iron and molybdenum species on the surface of the catalyst. Appropriate acidity of ammonium molybdate solution can optimize the ratio of MoO₃ and Fe₂(MoO₄) species on the catalyst surface, and improves the catalytic oxidation performance, which is conducive to the improvement of yield and selectivity of formaldehyde.