The invention discloses a method for preparing benzaldehyde by catalytically oxidizing phenylcarbinol through Pt/BiOCl-metal oxide serving as a catalyst. The method comprises the following steps: by taking a noble metal Pt/BiOCl-metal oxide compound system as the catalyst, dispersing phenylcarbinol and the catalyst into water, and continuously stirring under a relatively low-temperature dark condition for 3 to 10 hours, wherein the generation selectivity of the benzaldehyde can be 99 percent or above, and the yield of the benzaldehyde is retained within a range of 80 to 100 percent according to different types of carriers. The method has the following active effects that 1, the reaction can be carried out at relatively low temperature, such as room temperature of 25 DEG C; 2, low-cost air is used as an oxidant, so that the problem of environmental pollution caused by the fact that a high-cost metal such as chromium and manganese is used as the oxidant is solved; 3, no alkaline substances serving as an auxiliary catalyst are added into a reaction system; 4, basically no side effect is caused in a reaction process, and the generation selectivity of the benzaldehyde is retained at 99 percent or above; 5, equipment devices for reaction and an operation process are simple.