Aiming at the problem of multi-directional strain measurement, we design a trifarious fiber Bragg grating (FBG) strain sensor based on a boss and a ring-shaped substrate structure. We realize the simultaneous measurement of the strain in three directions of the structure. Static contrast and vibration monitoring experiments with resistance strain gauges were conducted using the vibration testing machine and stainless steel plate. The results show that the static strain curves of the FBG sensor and strain gauge in three directions are the same. Additionally, the correlation coefficients are 0.98, 0.98, and 0.99, respectively. The results of vibration power spectrum analysis show that the FBG sensor and strain gauge can observe the first and second harmonics; the frequency error is 2.77% and 0.97%. Furthermore, the strain gauge can detect high harmonic signals. The sensor has many advantages, such as simple structure, small size, high accuracy, and accurate location, having a promising application future in multi-directional strain monitoring.