This study focused on the in-situ mixing process of middle-pressure jet grouting method of 20 MPa or less and aims to establish a computer-aided engineering (CAE) system that can simulate the performance on a computer from the planning/design stages. This ground improvement method is the combination of a jet grouting method and a jet grouting with mechanical agitation and mixing method having been put into practical use. These two ground-improvement processes were computationally reproduced here using the moving particle semi-implicit (MPS) method which is capable of handling ground failure phenomena and high-velocity fluids and construction specifications were examined according to the ground conditions. In order to confirm its effect, a comparative analysis was performed with different jet pressures, development situation was visualized, and its performance was evaluated. The results show that the cement slurry jet ratio in the planned improvement range, including the periphery of the mixing blade was increased and a high-quality columnar soil-improved body was obtained. It is expected that the introduction of CAE will contribute to the visualization of the ground, and that CAE will be an effective tool for the visual management of ground improvement method during and after the construction.