Abstract: The welding stress and strain were investigated using the finite element method combined with the experiments. The research results showed that the metal in the melting pool is melted in the frame of area with compressive plastic strain, and cooled down also in the frame of the area with compressive plastic strain. The tensile plastic strain is produced in the weld when it is in the state of 'mechanical melting' during the cooling process. But in the residual state, the compressive plastic strain still remains in the weld. The peak value of longitudinal tensile stress in the weld of titanium alloy is always lower than its yield strength at the appropriate temperature during the cooling process, this situation is kept until the residual state.