Abstract: Based on laser deep penetration brazing process,a CW ROFIN-SINA laser with a output power of 3.5 kW was used to join aluminium and titanium alloys with a thickness of 3 mm.The aluminium melted by the focused laser beam deep penetration was wet the interface of titanium to form a brazing joint.The tensile test results show that the fracture happens on the interface,and incomplete fusion parts on the interface are observed with an Olympus metallographic microscope.Through studying the influence of process parameters on the incomplete fusion rate,the fusion of the interface will be improved by reducing the welding speed and optimizing the beam spot offset,defocusing distance and deflexion angle of laser.