A zero-strain soil pressure sensor includes a shell provided with a hydraulic oil cavity and a cavity located below the hydraulic oil cavity, a processor, an outer elastic film arranged at the upper end of the hydraulic oil cavity, an inner elastic film arranged between the hydraulic oil cavity and the cavity, an outer strain bridge circuit connected with the outer elastic film, an inner strain bridge circuit connected with the inner elastic film, a piston communicated with the hydraulic oil cavity, and a driving mechanism connected with the piston. The outer strain bridge circuit, the inner strain bridge circuit and the driving mechanism are electrically connected with the processor. The invention has the beneficial effect that the piston is driven by the driving mechanism to control the oil pressure in the hydraulic oil cavity, external soil pressure is balanced through the oil pressure to keep the outer elastic film in an non-deforming state all the time, and only the inner elastic film is deformed, so tha
