Railway line structure additionally arranged in existing railway land boundary and train operation method

The invention discloses a railway line structure additionally arranged in an existing railway land boundary and a train operation method, which greatly improve the transportation capacity of railway lines and the use efficiency of urban central passenger stations on the premise of not changing the existing railway land boundary, and overcome the two technical problems of large land acquisition and demolition quantity and transportation cross interference. A newly-built frame structure for bearing the load is arranged in the existing railway land boundary of the existing first railway line and the existing second railway line and below the existing first railway line and the existing second railway line, and a newly-built first railway line is arranged in the newly-built frame structure and below the existing first railway line. A newly-built second railway line is arranged below the existing second railway line; a double-layer line station composed of ground line stations and underground lines is arranged on