Abstract: In this paper, with the help of high performance infrared thermal imager, local hot spots of nugget and plastic ring on the side of SUS301L stainless steel of the SUS301L-Q235B dissimilar materials spot-welded joint was monitored. And the quantitative relationship between the temperature rise slope and the fatigue limit of the welding joint of dissimilar materials was established. Then, a method to predict the fatigue limit of the spot-welded joint of dissimilar materials based on the tipping point of temperature rise. The results show that a serious nugget migration generates on the Q235B side of SUS301L-Q235B dissimilar materials spot-welded joint, which results in reduction of the carrying capacity of stainless steel. Under the action of high frequency shear tensile, the "four stages" temperature evolution characteristics are presented. The fatigue limit predicted by infrared thermography was 5.569 kN. The fatigue limit obtained by the traditional staircase method was 5.875 kN. The error between the predicted value and the test value was 5.21%, which presents a high concordance. The rapid fatigue limit prediction proposed in this paper can overcome the limitations of the traditional fatigue test method and realize non-contact and non-destructive prediction of spot-welded joint fatigue limit of dissimilar materials, which has important engineering significance and research value.