<p>This work uses thermal mechanical processing (TMP) to optimize the grain boundary character distribution (GBCD) of grain boundary engineering (GBE) in face-centered cubic CoCrFeNi high-entropy alloy. Large-quantity low ΣCSL grain boundaries, among which Σ3ⁿ grain boundaries are the main body, and triple junctions, which generated by the interaction between Σ3ⁿ grain boundaries, can disrupt the connectivity of high-angle grain boundaries, thereby achieving GBCD optimization. During the deformation process, CoCrFeNi mainly undergoes dislocation slip and twin, and the amount of deformation twins increases with the deformation degree. This is beneficial for the formation of annealing twins in the subsequent annealing process, resulting in increase in low ΣCSL grain boundaries. Through the study of the influencing factors of GBCD, such as deformation amount, annealing temperature and annealing time, it is found that the content of low ΣCSL grain boundaries and triple junctions increases during recrystallization but decreases during grain growth. GBCD was optimized, at a rolling reduction of 60%, an annealing temperature of 800°C, and an annealing time of 60 minutes, when CoCrFeNi exhibits the lowest connectivity for high-angle grain boundaries, which suggesting that the HEA GBCD can be optimized by GBE.</p>