Abstract: AA5754 and AA6082 aluminium alloy are two kinds of aluminius alloys with different strengthen modes. In the processing of the resistance spot welding, the microstructure of the two aluminium alloys changes in different types. By two different numerical models, the microsturcture proportion in the nuggets of the two aluminium alloys was simulated and pridicted. Conpared with the experimental results, the two simulation models are effective to predict some important phenomenas in terms of the phase transformation of the nuggets. Both the simulation results and the experimental results show that there are marked different features in the phase transformation of the two kinds of aluminium alloys.