The invention relates to a catalyst for catalyzing direct oxidation of toluene to prepare benzaldehyde and a preparation method thereof. The catalyst comprises the following components in percentage by weight: 85 to 90 wt% of magnesium oxide and alumina composite oxide carrier; 0.5 to 10 wt% of cerium, 0.5 to 5 wt% of cobalt, 0.1 to 5 wt% of copper, and 0.5 to 2 wt% of nickel, wherein the mole ratio of magnesium oxide to alumina is 1-2. The catalyst takes a mixture of magnesium oxide and alumina as the carrier, can directly catalyze the oxidation of toluene to prepare benzaldehyde, and has the advantages of high toluene conversion rate, high benzaldehyde selectivity, high reaction stability, excellent performance, and mild reaction conditions. Moreover, the reaction product and the reactants are in two phases, and thus separation and purification become easier.