The topological evolution and annihilation mechanism of the three-, four- and five-sided grains are studied by using the phase field crystal (PFC) model. Both the large-angle and small-angle grain boundaries are discussed during the grain annihilation process. The results show that for the large-angle grain boundaries, grain annihilation is achieved through grain boundaries migration and absorption by triple junction. For the small-angle grain boundaries, the grain annihilation is achieved by dislocation slip, reaction, and absorption by triple junction. However, when the number of sides of a grain increases to seven, the grains show obvious growth instead of annihilation. Two kinds of growth mechanisms for the seven-sided grain are obtained by simulating the growth process. The effects of the number of grain sides on the evolution of grain annihilation are explored. These results are consistent with the Von Neumann-Mullins model and Euler formula.

利用相场晶体（PFC）模型研究了三边、四边和五边晶粒的拓扑演化和湮灭机制。在晶粒湮灭过程中讨论了大角度和小角度晶界。结果表明，对于大角度晶界，晶粒湮灭是通过晶界迁移和三结吸收来实现的。对于小角度晶界，通过位错滑移、反应和三结吸收实现晶粒湮灭。但是，当晶粒的边数增加到七个时，晶粒表现出明显的生长而不是湮灭。通过模拟生长过程，得到了七边形晶粒的两种生长机制。探讨了晶粒边数对晶粒湮灭演化的影响。这些结果与冯诺依曼-穆林斯模型和欧拉公式一致。