Research methods: The main research contents include: (1)the experimental research of dynamic characteristics of subgrade bed of ballastless track; (2) the experimental research of techniques against foundation settlement which focuses on pile-net subgrade and pile-plank subgrade; (3)the research of rationality of using red beds as fillings for subgrade of ballastless track; (4) the research of stiffness matching of under-rail foundation of ballastless track. In this paper design and construction of subgrade in comprehensive experimental section of ballastless track on Suining-Chongqing line based on the experimental research, three key technologies of ballastless track subgrade of passenger traffic special line are discussed, which include the control of foundation settlement, the longitudinal stiffness matching of under-rail foundation, and the rational use of not-fine subgrade materials.