At present, the "2nd, 3rd, 4th and 5th" generations of mobile communication networks are operating at the same time, and mobile operators face a series of problems ,including income slowdown, rapid growth of investment and expenditure, and cash flow pressure, etc. Therefore, the frequency of low-generation networks must be cleared. However, there are many obstacles in quitting the network, including users' rights and interests, Internet of Things service migration and spectrum allocation. According to the global experience of quitting the network, the basic conditions for quitting the network of low generations are summarized to avoid the shock caused by quitting the network. Meanwhile, mobile operators also need to work out reasonable steps to make the network of low generations quit smoothly.