The classical preload design method of combinational frame of hydraulic presses is based on the assumption that the beams of the frame are rigid and the column of tie rod has only axial deformation, which is not agreed with practice. In order to eliminate the unbalance load of a 100 MN hydraulic press after installation, the distribution law in prestressing in instalation of the combinational frame was researched, and the tie rod preloads and degression law of preloading were obtained. According to the results of material mechanics, finite element and experimental analysis, the aim of the installed hydraulic press was implemented that the upper beams are not unblanced, and are only moved vertically.