Abstract: With 2195 Al-Li alloy joints by friction stir welding as research objects, the numerical simulation of brittle fracture based on the phase field method was carried out. Based on the Francfort-Marigo variational principle, the phase field method considered the fracture energy in the total potential energy of the system. It considered the tension and compression of the strain energy. The dispersion crack model was introduced to approximate the non-smooth crack topological relationship, and the material damage was characterized by order parameters. Based on the Abaqus and user element subroutine (UEL), the coupling of the displacement field and phase field was realized by alternate solutions to solve the brittle fracture problem. Compared with the experimental results, the simulation of the crack propagation path of brittle fracture in the welding zone of the compact tension specimen based on the phase field method was in good agreement, and the maximum load error was only 0.46%. The effects of incremental step length ∆u, phase field feature width L_c, and mesh size h on the simulation results of the phase field method were studied. The phase field method was compared with the extended finite element method (XFEM) and the cohesive zone model (CZM). The results have shown that when the analysis increment step is 10⁻⁴, the analysis results converge. When L_c is twice the crack h, the simulation results are relatively accurate. The phase field method can accurately simulate the brittle fracture evolution of 2195 Al-Li joints by alloy friction stir welding.