The fission and fusion of mitochondria is the main way of dynamic changes of mitochondrial membrane, and it is also an important means to maintain the normal function of mitochondria. The mechanism of mitochondrial fission used to be based on fluorescent-labeled optical microscopy imaging. Due to the limitation of resolution, it is not possible to directly observe the ultrastructural characteristics of the mitochondrial fission. Cryo-electron tomography (cryo-ET) obtains more realistic structural information by maintaining the physiological state of the sample as much as possible. In this article, we use cryo-ET to study the membrane dynamic of mitochondrial fission in primary hippocampal neurons. By imaging the spontaneous mitochondrial fission, we found that both central and peripheral mitochondrial fission have contact with the endoplasmic reticulum (ER). It is worth noting that we have also found that some mitochondria will separate the outer mitochondrial membrane from the inner membrane, forming a "matrix-free" area. All these may show a way of mitochondrial quality control.