In China, 4G and 5G networks have been maturely applied to high-speed rail scenarios, and the user experience of networks on high-speed rail has been further improved. The critical issues of wireless communication coverage on high-speed rail have been solved with key technologies, including Doppler frequency offset fixed by shift correction and compensation algorithm, frequent switching of networks solved by the exclusive network coverage method and cell combination technology, and car body attenuation resolved by combining multiple frequency networks and prioritizing low frequency. This paper analyzed such key technologies and verified their effects on problem-solving via tests. With the popularization of high-speed rail, new problems have emerged in the communication field, such as complex networks with multiple formats and multiple frequencies, the influence induced by exclusive network coverage for high-speed rail, and the problem of insufficient capacity. This paper explored two topics, namely the breakpoint issue and capacity problem of the exclusive network when trains pass each other on high-speed rail, and proposed a solution of 4G and 5G fusion coverage to achieve continuous coverage at breakpoints and equalize capacity resources, which expanded the application of 5G on the basis of fully harnessing the 4G network.