Abstract: Mixed crystal or non-uniform structure of superalloy forgings will lead to the degradation of material properties. Effective ultrasonic nondestructive testing method can be used to evaluate the homogeneity of superalloy structure. Because the homogeneity of structure affects the propagation of ultrasonic signals in materials, the scattering noise distribution of ultrasonic waves in superalloy materials can reflect the structural differences of materials. Taking a certain grade of superalloy forged bar as research object, the ultrasonic data acquisition was carried out based on the multi-channel ultrasonic automatic detection system of bar, and the noise signal of each depth was analyzed under the sensitivity condition equivalent to φ0.8 mm flat bottom hole. According to the microstructural data of the corresponding positions by ultrasound detection, the average value of noise signal is positively correlated with the grain diameter in the 99% confidence interval, and the standard deviation of noise signal is positively correlated with the variation coefficient of grain diameter in the 95% confidence interval. Further cluster analysis can confirm that when the average noise is 1.6%-1.79% and the standard deviation of noise is 0.6-0.8, the material is mixed crystal structure. When the average noise value is 1.81%-2.6%and the standard deviation of noise is greater than 1, the material contains dendritic structure.