Aiming at the problem of insufficient bearing capacity of in-service pile foundation in silty clay stratum, numerical simulation and field test were used to realize the parameter design and reinforcement effect evaluation of in-service pile foundation grouting. The expanding form of split grouting vein was analyzed, the finite element model of grouting pressure transmission was established by applying volume strain to the vein, the distribution law of radial pressure on the pile side in silty clay stratum under different grouting conditions was studied, and the design method of grouting parameters was put forward. The attenuation of earth pressure with distance was nonlinear. Under certain soil parameters, when the grouting pressure was 2.0 MPa and the distance between grouting hole and pile side was 0.5 m, the radial pressure transmitted to pile side was larger. At the same time, taking the pile foundation in the reconstruction and expansion site of Beijing-Taibei Expressway as a model, the contour map of the increase range of pile foundation bearing capacity under different working conditions was drawn, and the pile foundation bearing capacity was increased by 30.3%-89.4% after grouting reinforcement, which provided reference for the reinforcement effect of in-service pile foundations.