This study investigates the fatigue performance and dislocation evolution mechanisms of nanoscale nickel-based superalloys at cryogenic temperatures. Utilizing molecular dynamics simulations, we examined how grain number, strain amplitude and the number of cycles affect the fatigue behavior of these alloys. Shear strain contour maps and atomic structure evolution maps were employed to conduct a quantitative analysis of the fatigue process at 77K, considering various grain numbers (ranging from 100 to 300) and strain amplitudes (spanning from 50Å to 100Å). The findings reveal that an increase in grain number reduces the range of shear strain concentration, with the concentrated regions extending from the sample notch to the sides. Larger strain amplitudes and more cycles amplify the range and degree of strain concentration and promote the extension of strain-concentrated areas toward the sides. Additionally, increased strain amplitude results in a higher proportion of BCC atoms, while FCC atoms remain the dominant structure. The grain number significantly influences dislocation evolution maps; with grain numbers exceeding 150, there is an increase in the formation of dislocation walls and loops, and a reduction in dislocation numbers in the notch area. Furthermore, as the strain amplitude increases, there is a decreasing trend in the total dislocation count, while the length of 1/2〈110〉 (Perfect) dislocations increases significantly. The maximum density of 1/6〈112〉 (Shockley) dislocations for a grain number of 250 is substantially higher than that for other grain numbers, about 1.55 times greater than the density for a grain number of 300. [ABSTRACT FROM AUTHOR]