The invention discloses a steam cylinder interlayer structure. The steam cylinder interlayer structure comprises an outer cylinder and an inner cylinder arranged in the outer cylinder in a sleeving manner, wherein the front end of the inner cylinder is a steam intake side, and the rear end of the inner cylinder is a steam exhaust side; a steam leakage channel is arranged close to the front part of the inner cylinder, and communicates an interlayer between the inner cylinder and the outer cylinder with intake steam of the inner cylinder; a gap is reserved between the rear end of the inner cylinder and the rear end of the outer cylinder, and a main flow channel for exhaust steam is isolated from an interlayer between the inner cylinder and the outer cylinder through a sealing element; and a plurality of tunnels are formed in the peripheral direction of a cylinder wall of the inner cylinder, the inlets of the tunnels are located in one end part of the steam exhaust side of the inner cylinder, and the outlets of the tunnels are located in an inner side surface close to the middle part of the inner cylinder. According to the steam cylinder interlayer structure disclosed by the invention, the sealing element (for whole-ring sealing) connecting the inner cylinder with the outer cylinder is added to the tail part of a steam cylinder, so as to prevent a steam flow in the interlayer from being merged in a steam exhaust area of the main flow channel. The tunnels are formed in the wall of the inner cylinder (the plurality of tunnels are uniformly arranged on the peripheral section of the wall of the inner cylinder), and the steam flow in the interlayer is introduced in the main flow channel in a certain stage. A work-applying capacity of steam in the interlayer is recovered, and the economical efficiency of a unit is increased.