A precise bearing capacity calculation method for a hydrostatic guide rail mainly includes the steps that a cutting load F and an oil cavity bearing capacity fi act on the guide rail and a sliding plate together; the cutting load F is divided into 6 component loads Fx, Fy, Fz, Mx, My and Mz, and the component loads are sequentially applied to the guide rail and the sliding plate; the oil cavity bearing capacity Fxfi is calculated when oil cavities together bear the component load Fx; in the same way, the oil cavity bearing capacities Fyfi, Fzfi, Mxfi, Myfi and Mzfi are calculated when the oil cavities together bear the other component loads Fy, Fz, Mx, My and Mz; the bearing capacity components Fxfi, Fyfi, Fzfi, Mxfi, Myfi and Mzfi are superimposed, and the final bearing capacity fi of the oil cavities is obtained. The method can achieve automatic calculation according to the distribution structure of a bearing pad of the hydrostatic guide rail, is suitable for various complex structures and complex oil cavity distribution modes, has certain universality and can be implemented through automatic calculation of a computer, and calculation precision can be automatically adjusted according to a calculation mode and a calculation tool.