Abstract: For the laser welding of aluminium alloys，according to the model of the two-dimensional transient temperature field，analytical equation was obtained to calculate the temperature gradient．The orthogonal optimization experiment was designed under the laser power，defocusing distance and the welding speed，and the optimum process parameters were obtained．Using the formula of the Matlab，the temperature gradient curve was calculated．The transient temperature decrease as the distance is far from the weld．The temperature near the welds was tested by using the thermal test paper，the test result was in accordance with the calculated result．