Abstract: Model for laser welding of TC4 titanium alloy thin sheet was established. The effects of sheet width on welding residual stress and instability deformation of titanium alloy sheet were analyzed by finite element method. The results show that the maximum longitudinal residual tensile stress appeared in the heat affected zone on both sides of the weld center. With the increase of sheet width, the average residual compressive stress and critical instability force decreased. The instability deformation thin of the titanium alloy degree sheet along the welding direction decreased with the increase of sheet width, while that perpendicular to the welding direction increased with sheet width increasing. When the sheet width was 120 mm, The distribution of instability deformation degree of the sheet was saddle-shaped. When the sheet width was 320 mm, the saddle-shaped deformation distribution characteristic disappeared. The relative error between the experimental value of z-direction displacement and the simulation of the instability deformation of titanium alloy thin sheet was 8%, indicating that the simulation was relatively accurate.