The invention discloses a submarine pipeline internal detecting device and belongs to the technical field of pipeline leakage detecting. The problems that in the prior art, an internal detecting device cannot adapt to detection of large-deformation pipelines, and is poor in adaptivity and passing ability. The submarine pipeline internal detecting device comprises an anti-collision power supply mechanism, a floating mechanism and a posture and mileage measuring mechanism which are rotatably connected in sequence. The floating mechanism comprises a magnetic circuit module and a central framework, wherein the outer edge of the central framework is sleeved with the magnetic circuit module, the magnetic circuit module floats two-dimensionally relative to the central framework, and the magneticcircuit module is always attached to the inner wall of a pipeline. The magnetic circuit module is used for generating a magnetic field so as to generate flux leakage signals for flaw pipelines. The submarine pipeline internal detecting device can be used for pipeline internal detection.