Three-dimensional (3D) tension sensor based on fiber Bragg grating (FBG) is used to test the installation state of high-voltage bushing in substations, and the stress state of the bushing end is continuously monitored for 1500 h. By measuring the stress at the end of the bushing under different kinds of installation, the arrangement of the down line and fittings installation type are optimized. By monitoring the stress at the end of the bushing for a long time, the 3D tension and the thermal stress due to temperature changing at the end of the bushing are measured. Low-frequency signals (0.18 and 0.22 Hz) are obtained from the 3D tension, which are due to substation shaking resulting from the wind load on the cross line. The health monitoring of the substation is preliminarily realized by the 3D tension sensor based on FBG, which can further facilitate the development of the smart grid.