The invention discloses a method for preparing high-purity m-cresol by selectively oxidizing mixed m-cresol and p-cresol. The method comprises the following steps: putting mixed m-cresol and p-cresol,a catalyst, sodium hydroxide and a solvent into a container, stirring, heating to a reaction temperature, continuously introducing oxygen to react, adding water, distilling to recover the solvent toobtain a mother solution, acidifying, adjusting the pH value, cooling, crystallizing, and filtering to obtain filter cake which is p-hydroxybenzaldehyde sodium salt and a mother solution which is a m-cresol sodium salt solution; dissolving and acidifying the p-hydroxybenzaldehyde sodium salt, adjusting the pH value, cooling, crystallizing and filtering to obtain filter cake that is a wet p-hydroxybenzaldehyde product, and drying to obtain a finished p-hydroxybenzaldehyde product with the purity of higher than 99.2%; acidifying the m-cresol sodium salt solution, adjusting the pH value, collecting an oil phase m-cresol crude product, and putting the oil phase m-cresol crude product into a tower kettle of a rectifying tower; starting magnetic stirring in the tower kettle for stirring, starting a high-vacuum mechanical pump for pressure reduction, starting tower kettle heating, and collecting a front distillate, a main distillate and a rear distillate. The obtained main distillate is an m-cresol finished product with the purity of higher than 99.5%.