The establishment of intelligent high-speed railway architecture promotes the continuous and in-depth development of intelligent construction technology of railway engineering; meanwhile it puts forward higher requirements for reliability, real-time and comprehensiveness of data. 5G communication is characterized by high speed, low delay and wide connection, which can provide communication infrastructure support for intelligent railway construction. This paper analyzes the overall architecture and development trend of intelligent construction of railway engineering and puts forward the application requirements of 5G in intelligent construction of railway based on the characteristics of 5G communication technology through analysis. From the work above, this paper further proposes the construction scheme of intelligent subgrade site integrating 5G. The relevant results in the paper can provide reference for intelligent upgrading of railway and related engineering construction.