An intermediate useful for the synthesis of an SGLT inhibitor and a method for preparing an SGLT inhibitor are provided. By employing an intermediate having Chemical Formula 5, the difficulty of purification with existing processes can be solved, the quality requirements for related substances can be achieved with only one purification step, and the quality control problem in each step can be solved by performing several steps in situ. A method for synthesizing a compound of Chemical Formula 1 by using a compound of Chemical Formula 5 enables purification in an earlier step, thereby solving the problems of existing synthesis processes, in which the quality requirements for related substances were difficult to control step-by-step due to a continuous process, thereby minimizing the amount of related substances in the final product. In addition, the yield of a diphenylmethane derivative according to Chemical Formula 1 is increased.