The invention provides a method for preparing m-chlorophenol. The method comprises the following steps: adding m-chloroaniline and a sodium nitrite solution into a mixture of silica-loaded sulfuric acid catalyst and water, cooling, and performing diazo-reaction to obtain a diazonium salt solution, wherein the weight ratio of the m-chloroaniline, the sodium nitrite solution, the silica-loaded sulfuric acid catalyst and water is 2:(3-4):(6.5-8):(7-8); adjusting the pH value, and filtering to obtain filtrate; adding the filtrate into the mixture of silica-loaded sulfuric acid catalyst and water,performing hydrolysis reaction, wherein the weight ratio of the filtrate, the silica-loaded sulfuric acid catalyst and water is (9-13):(2-3):1; and performing extraction layering and distillation to obtain m-chlorophenol. According to the preparation method, the m-chlorophenol yield is 80 percent or more and is easy for industrial large-scale application; the silica-loaded sulfuric acid catalyst slowly releases concentrated sulfuric acid adsorbed in a silica body in the reacting process; the silica body can repeatedly absorb and utilize remained concentrated sulfuric acid remained after the catalyzing reaction, and waste acid output is remarkably reduced.