The invention discloses an optimized design method of three-point support positions of a machine tool body. As for a T-shaped machine tool body adopting crossed rib plates inside, the optimized design method comprises steps as follows: (1) a mechanics model of three-point support of the T-shaped machine tool body is established through equivalent simplification of a machine tool body model; (2) the positions of key points of deformation are found on the mechanics model of the machine tool body, and a deformation expression of each key point is derived; (3) the three-point support positions of the mechanics model under the optimal static stiffness condition are obtained by combining the deformation expressions of all the key points; (4) design variables, variable space and objective functions of a multi-objective optimization problem of three-point support are determined; (5) parametric modeling is performed on the machine tool body by the aid of CREO software; (6) static and dynamic analysis is performed on the machine tool body by the aid of ANSYS software; (7) a multi-objective optimization platform is set up for optimization, and optimal three-point supporting position parameters are obtained. The optimal static stiffness of the machine tool body can be obtained, and the purpose of improving the dynamic stiffness of the machine tool body is achieved.