Abstract: Aimed at the root fatigue failure propagation path problem of T-joints in Q355B low alloy steel, an equivalent stress intensity factor (KEQ) method based on force analysis and calculation was proposed to predict the root crack propagation angle. The maximum error of solving the stress intensity factor is less than 5% verified by finite element simulation. Compared with the maximum circumferential stress method (MCS method) and the effective structural stress method (ETS method) based on finite element analysis, and combined with the bending fatigue test results of three different stress levels, it is found that: The crack propagation angles calculated by equivalent stress intensity factor method, maximum circumferential stress method and effective structural stress method are 25.6°, 25.9° and 32.2°, respectively. Compared with the root crack propagation angle of 24° in the actual fatigue test, the errors are 6.67%, 7.92% and 34.17%, respectively. The results show that KEQ method has the highest accuracy in solving crack propagation angle, which is more suitable for predicting the root crack propagation angle of T-joint fillet weld under bending fatigue loading.