The research in the area of grain boundary engineering was mainly focused on the relationship between process, microstructure and properities. However, little attention has been paid to the formation and evolution process of low ∑CSL grain boundary. To better understand the dynamic process, electron backscatter diffraction (EBSD) was used to analyse the grain boundary migration and evolution in J75 alloy. Single-step deformation heat treatment with 5% pre-deformation and 1000 °C annealing was used to increase the proportion of low-∑CSL grain boundary to over 70%, and formed grain clusters with ∑3n orientation relationship to break the connectivity of random grain boundaries. During the annealing process, the migration ability of ∑3ic grain boundary is strong, and when it encounters other ∑3, ∑9 would be formed; In addition, ∑3 with ∑9 would lead to∑3+∑9→ ∑27 or ∑9+∑3→∑3 processes, and the latter was more likely to occur. The ∑3 regeneration was closely related to the ∑3ic grain boundary; A mechanism for breaking the connectivity of random grain boundary network was proposed. When random boundary met low ∑CSL grain boundary, R/∑ grain boundary would form. If the ratio (R/∑)≤29, the connectivity of random grain boundary network could be interrupted.