A dual-mode fiber Bragg grating soil pressure sensor is invented on the basis of dual membrane oil cavity structure. Biasing pressure experiments are done with this kind of soil pressure sensor. The results show that the sensor can effectively distribute the soil pressure between the sensor and its contacting segment evenly. Under soil pressure

the first diaphragm deflection passes the pressure on to the second diaphragm via transferring pressure oil. The transfer lever and the equal strength cantilever are rigidly connected. The central deflection of the second diaphragm pushes the transfer lever timely

which exerts a equal size defection on the free end of the equal strength cantilever. Then soil pressure could be obtained by the wavelength shift of fiber Bragg grating

which is pasted on the surface central axis of equal strength cantilever. The loading experiment indicates that the sensitivity of dual-mode optical fiber Bragg grating soil pressure sensor is 412.7 pm/MPa; the nonlinearity error is 1.97% FS; and the repeatability error is 3.68% FS.