The invention relates to a deep water area settlement monitoring device and an application method. The deep water area settlement monitoring device comprises a standard pile assembly, a settlement pressure probe assembly and a reading instrument. The standard pile assembly comprises a standard pile. The end of the standard pile is provided with a settlement ruler, and the end of the settlement ruler is provided with a gas pressure correction probe. The settlement pressure probe assembly comprises a probe water circulation connection way, a settlement probe and a settlement plate. One end of the probe water circulation connection way is connected with the standard pile, and the other end of the probe water circulation connection way is connected with the settlement probe. The probe water circulation connection way is located blow the gas pressure correction probe, and the settlement probe is fixed into the settlement plate. The gas pressure correction probe and the settlement probe are connected with the reading instrument. The deep water area settlement monitoring device is simple in structure, capable of effectively ensuring the precision of settlement monitoring, low in price, safe, reliable, capable of being applied to sludge soft soil foundation monitoring projects such as the water conservation project, the ocean project and the soil engineering project, high in practical application value and capable of performing automatic monitoring through a computer.