A system and a method for preparing cycloalkanone are provided. The method includes the steps of: (a) oxidizing cycloalkane to form a mixture containing ketone, alcohol and unreacted cycloalkane; (b) adding to the mixture alkali metal hydroxide or alkali metal carbonate to form a first mixed solution; (c) separating the first mixed solution into a first organic phase solution and a first aqueous phase solution; and (d) extracting the first organic phase solution by water to obtain a second organic phase solution and a second aqueous phase solution; and (e) distilling the second organic phase to separate out cycloalkanone. The method performs phase separation after a mixing step, and then performs water extraction, thereby effectively lowering the contents of the metal salts in the organic phases. Compared with acid-water extraction, the method not only provides better cooling effects but also reduces equipment corrosion, and therefore has the advantage of decreasing the need for sewage treatments.