The invention relates to a deep sea underflow change observation device based on differential pressure measurement. The deep sea underflow change observation device comprises a differential pressure sensing cabin, a base, a controller and a floating body releasing device. The differential pressure sensing cabin and the base are connected through a connection portion; the controller is arranged inthe connection portion; a floating body is arranged in the differential pressure sensing cabin and is released by the releasing device; and the releasing device is arranged between the floating body and the differential pressure sensing cabin. The differential pressure sensing cabin comprises a hydrostatic pressure cabin and an environmental water pressure cabin. The top portion of the environmental water pressure cabin is communicated with the hydrostatic pressure cabin, and the communicated place is blocked by a spring sheet. The spring sheet is internally provided with an optical fiber sensor. The hydrostatic pressure cabin is always communicated with sea water. The environmental water pressure cabin is always communicated with the water in a sea-bottom deposition layer. The releasing device comprises an electric capstan. The electric capstan is provided with an acoustic signal device. The base is provided with a soil pressure sensor and a counterweight member. The optical fiber sensor, the acoustic signal device and the soil pressure sensor are connected with the controller; and differential pressure of a place can be measured based on feedback of each sensor. The device can reduce the influence of deep sea underflow, and can observe changes of seabed underflow more accurately.