The invention discloses a seabed surface settlement observation device and a measurement method, and belongs to the technical field of seabed observation. The seabed surface settlement observation device comprises a pressure resistance cabin, a reference pressure cabin, a pressure relief end cap and a pressure difference sensor, wherein one end of the pressure resistance cabin is communicated withthe outside; the reference pressure cabin is communicated with the other end of the pressure resistance cabin; the reference pressure cabin is provided with a pressure relief hole; the pressure relief end cap is arranged on the pressure relief hole to carry out sealing and pressure relief on the reference pressure cabin; and the pressure difference sensor is positioned in the pressure resistancecabin and seals two ends of the pressure resistance cabin to detect a pressure difference between the interior of the reference pressure cabin and the outside. By use of the seabed surface settlementmeasurement method, the above seabed surface settlement observation device is adopted for measurement. Initial pressure in the reference pressure cabin and the pressure of the measurement point underan initial state are the same, pressure measured by the pressure difference sensor is a pressure difference generated by a seabed surface sinking distance, the measuring range of the pressure difference sensor is reduced, and a measurement result is accurate.