Disclosed is a method for preparing methyl methacrylate (MMA), the method including: (1) separating isobutene containing saturated hydrocarbon (n-butane and iso-butane), via a catalytic distillation process from a stream of C4 hydrocarbons containing butadiene, n-butene, and isobutene; (2) producing methacrolein via a first oxidation reaction of the separated isobutene; (3) producing methacrylic acid via a second oxidation reaction of the produced methacrolein; and (4) esterifying the produced methacrylic acid with methanol. By having a high heat capacity, the amount of nitrogen added is minimized to reduce the size of the reactor and the amount of gas production at a rear end, which has a high economic feasibility due to the effect of reducing investment and investment cost.