The invention discloses a seabed sediment pressure observation device and method, and belongs to the technical field of seabed detection. The seabed sediment pressure observation device comprises a detection rod, a conical tip, a reference pressure cylinder and probes; the interior of the detection rod is hollow to form a containing cavity, and the detection rod comprises a section rods connectedwith one another; the conical tip is arranged at one end of the detection rod; the reference pressure cylinder is arranged at the other end of the detection rod, and comprises a cylinder body, an oilbag located in the cylinder body and a plug slidably connected with the cylinder body, and the plug selectively seals the cylinder body so that the oil bag provides constant pressure; and the probes are arranged between adjacent section rods respectively, each probe comprises a shell and a differential pressure sensor, a first channel communicated with an inner cavity of the oil bag is arranged inthe shell, the differential pressure sensor is used for detecting the differential pressure between a first channel and the outside, and the mechanical state in the sediment can be detected under thecondition of not being influenced by the seawater depth. The seabed sediment pressure observation method adopts the seabed sediment pressure observation device.