Since the existing soil pressure box sensor has low accuracy for monitoring the main lateral soil pressure outside the foundation pit wall, and inability to achieve three-dimensional soil pressure monitoring, a three-dimensional soil pressure sensor is designed based on the fiber Bragg grating (FBG) sensing device, containing six pressure surfaces and pressure diaphragms. This sensor has the capability to monitor the space's three-dimensional stress distribution with high sensitivity to monitor data, less liability to damage and long service life. Performance tests implemented on the produced prototype transducer and sensitivity is tested as 382.30769pm/MPa, 362.83692pm/MPa, 341.56308pm/MPa, 318.46154pm/MPa, 415.04615pm/MPa and 428.92308pm/MPa in the range of 0–3 MPa with lowest fitting error 0.99902. Moreover, the deviation of drift values for the measured wavelength to theoretically calculated value in the full range is nearly 2.3%, 1.6%, 0.49%, 1.6%, 0.4% and 1.3%. Consequently, this transducer meets the accuracy requirements of stress and deformation measurement for the structural health monitoring in civil engineering. To monitor the real-time deep soil pressure of the foundation pit wirelessly, four displacement sensors, which have been tested and calibrated, are installed in the foundation pit of the east square in the special-class station on Line 1 of Taiyuan rail transit. Subsequently, the reason for the change in the soil pressure on the monitored section is analyzed and compared with actual working conditions in the field verifying the effectiveness of the three-dimensional soil pressure sensing based on FBG in the soil pressure monitoring when constructing foundation pit.