Abstract: The interfacial fracture mode of dual phase steel(DP) weld greatly affects its mechanical performance and decreases its weld quality because much martensite in the nugget makes the welds brittle,but the traditional nugget diameter criteria is not suitable to estimate the quality of DP weld,and so this paper builds a mathematical mode based on macro-appearance and micro-mechanism to evaluate the different fracture modes of DP weld.Experimental results show that the model is effective on 1.4 mm and 1.8 mm DP600 welds and is also better than other evaluation criteria for their limited factors considered.