Abstract: In order to improve the detection ability of fatigue damage of selective laser melting GH4169 nickel-based alloy for vehicle, an efficient detection method based on nonlinear ultrasound was designed. The fatigue damage state of the specimen was accurately judged according to the nonlinear coefficient of ultrasound, and the fatigue damage of the alloy was rapidly measured by the high-order harmonic detection technology. Results show that the second harmonic wave has a lower amplitude than the fundamental wave. The specimen after 20, 000 fatigue tests shows signals with a larger amplitude of change in comparison to the initial specimen. Equiaxed crystals are formed in the microstructure of the sample, and most of the columnar crystals show strong directivity. A large number of fatigue cracks appear in the periodic fatigue samples. With the increase of fatigue period, the variation of nonlinear ultrasonic test is enlarged, forming similar variation characteristics. Compared with the test point at the neck contraction, the ultrasonic nonlinear coefficient at the horn mouth has a positive correlation with the fatigue cycle, but it only increases slightly. This study has a good theoretical support value for improving the fatigue damage detection accuracy of laser fused samples.