The structure optimization design of counterforce frame used in shield tunnel is carried out to improve its lightweight level and reduce its manufacturing and transportation cost. Firstly, the finite element analysis model of counterforce frame is established based on design structure, the loading conditions are determined by analogy of similar engineering data，and the stress and stiffness of counterforce frame are checked. And then, the main effect diagram is obtained by using variance analysis with taking all plate thickness as independent variables and total weight of the counterforce frame as dependent variable, and 5 kinds of plate thickness effecting on structure total weight largely are set as optimization variables. Finally, the particle swarm optimization (PSO) algorithm is used to calculate by taking 5 kinds of plate thickness as design variables, strength and stiffness as constrains, and minimizing the counterforce frame mass as object. The calculations results show that the maximum stress of the optimized structure is 252.2 MPa, the maximum deformation is 10.6 mm, the total mass of the counterforce frame is reduced from 305.78 t to 274.85 t, and the mass reduction ratio is 10.1% (30.9 t), which proves the effectiveness of the structure optimization.