This article summarized the structural analysis method and in-situ analysis method of the lithium ion secondary battery by using diffracted by neutron. Due to the interaction between neutron and nucleus, it can analyze the overall structure of the sample and can analyze a small amount of micro-phase at the same time. In addition, the neutron has a high penetration power and can be analyzed in situ in place in a non-destructive state. In addition, neutron ray photos can also be used to observe whether there is liquid or gas in the system. Therefore, the use of neutron diffraction to analyze the deterioration reaction, secondary phase of lithium ion secondary battery, and the problems that occur during the actual battery operation are very suitable methods.