In this research, a novel combined tri-dimensional accelerometer designed for vibration measurement in conventional rotating machinery is reported. The sensor utilizes a flexible hinge and fiber Bragg gratings (FBGs) which operates in three dimensions (3-D), allowing measurement along the X-axis, Y-axis, and Z-axis. The working principle and theoretical models of the sensor have been introduced and established. And then, the design and optimization of the sensor were achieved through nonlinear programming in MATLAB. To validate the theoretical resonant frequencies, Finite Element Method (FEM) analysis was employed, resulting in an accuracy that yielded an error of less than 5%. Experimental testing confirmed resonant frequencies of approximately 330 Hz, 350 Hz, and 560 Hz in the X-axis, Y-axis, and Z-axis, respectively, with sensitivities of 285.2 pm/g, 325.3 pm/g, and 202.2 pm/g within a frequency range of 0 Hz to 100 Hz. The sensor demonstrated a lateral interference level of less than 5.8% in all three-dimensional orientations. The high sensitivity and adaptability of the sensor make it suitable for monitoring mechanical equipment conditions, providing valuable insights for assessing the health and performance of rotating machinery.