Abstract: Microstructure and mechanical properties of laser lap weld joints of TC4 alloy are investigated.Experimental results show that the microstructure of joints is martensite α' crossed into basket shape in fusion zone.The average bearability of weld bead is 458 N/mm, and the maximal shear strength of interface is up to 732 MPa when the optimum parameters of laser lap welding for 0.8 mm thick TC4 sheet are P from 1800 to 2350 W and v from 1.5 to 2.5 m/min.The deflexion angle of joints is related to the bearability of weld joints, the bigger deflexion angle the better bearability of weld joints.