The effects of heat input on the laser beam welding residual stress and distortion of TC4 titanium alloy were investigated by finite element analysis and experimental tests. The internal relationships of residual stress, deformation and heat input were further investigated by the metallographic section of weld. The results showed that the tensile stresses produced in the longitudinal direction of welded joints were about 700 MPa-850 MPa, but only 50 MPa-80 MPa for the transverse tensile stresses. The tensile region of longitudinal residual stress was widened and the stress peak was decreased, but the magnitude of transverse tensile stress was increased when the heat input increasing. At the same time, the angular distortion was decreased and the transverse shrinkage deformation was increased when welding at above a critical specification. As the welding specimens were fully penetrated, the effects of heat input on the angular distortion were decreased.