Jet grouting technology is widely employed as a reinforcement of excavation base in soft soil area. Numerical analysis is carried out using PLAXIS 2D software. Firstly, the comparison of reinforced and unreinforced excavation is evaluated according to deformation, bending moment of diaphragm wall and ground settlement. The results show that the lateral deformation of diaphragm wall and ground settlement can be effectively reduced by basal grouting reinforcement in soft soil. Then four parameters, namely, the thickness of reinforcement zone, the penetration depth and stiffness of diaphragm wall and the thickness of soft soil layer, are analyzed and discussed. The reasonable thickness of reinforcement zone, the reasonable depth of diaphragm wall and the sensitivity of excavation deformation to the stiffness of diaphragm wall and the thickness of soft soil layer are obtained. It can provide reference and guidance for the support system design of similar projects.