Grouting pressure is down-hole pressure on the crack of grouting hole. Due to the constraints of grouting art, the grouting pressure is presented by the pressure of up-section of pipe, which produces measurement error of grouting pressure. the fluid flow model of grouting pipe for numerical computing is constructed, and orthogonal experimental method to analysis the error of grouting pressure influenced by cement grout ratio, grout velocity and grouting depth is adopted. And the significant factor is presented based on statistical method in different grouting conditions. The results demonstrate that grouting pressure is lower, the error of grouting pressure is bigger,and the relative error would exceed the up-bound precision of pressure sensor with 0.5%, and the measuring value must be revised. Secondly, the analysis of range results demonstrate conditions. The research results demonstrate that grouting pressure is lower,the error of grouting pressure is bigger,and the relative error would exceed the up-bound precision of pressure sensor with 0.5%, and the measuring value must be revised. Secondly, the analysis of range results demonstrate the grouting depth is the main factor of error,And the flow velocity of grouts is in sequence. The absolute error is bigger with smaller grouts ratio on the same grouting depth and flow velocity. Combining orthogonal test method and numerical computing, a computing method of grouting pressure in the grouting hole is presented.