The invention relates to an inner centering mechanism which is suitable for laying pipelines. The inner centering mechanism comprises a tractor, a storage pipe mechanism and an umbilical cable; the storage pipe mechanism is perpendicularly arranged on the tractor and is composed of a storage pipe, a guide trolley, an inner centering device, a pipeline sleeve and a horn-shaped connecting part; the storage pipe is through form top to bottom; the guide trolley and the inner centering device which can move up and down along the inner wall of the storage pipe are arranged in the storage pipe; the inner centering device is arranged under the guide trolley; the pipeline sleeve is arranged at the bottom of the storage pipe; the horn-shaped connecting part is arranged at the bottom of the pipeline sleeve; and the umbilical cable penetrates through the guide trolley from top to bottom and is connected with the inner centering device. The inner centering mechanism provided by the invention can rapidly and accurately finish inner centering of the pipeline when a subsea pipeline is vertically laid.