A novel fingertip three-dimensional (3D) force tactile sensor based on fiber Bragg grating is proposed and applied to crack detection. The sensor employs four FBGs combined with a sensitization structure, which optimizes the measurement sensitivity to axial and lateral forces while simplifying the decoupling process. The deformation characteristics under different forces were analyzed using a mechanical simulation, and a 3D force sensing model was constructed. The experimental results show that the sensitivities of the sensor in the X, Y, and Z directions are 1 680.45, 1 441.28, and 125.36 pm/N, respectively, which indicates the ability for 3D detection. In a dynamic experiment, the 3D partial force measured using the sensor is highly consistent with the theoretical value, and the maximum relative error of the combined force is only 4.40%. In the crack detection experiment, it exhibits good crack width detection and force monitoring abilities, and the maximum relative error of the detection width is less than 4%. The sensor is characterized by simple structure, easy decoupling method, and high sensitivity, which is highly applicable to crack detection and the repair tasks of robots in complex environments.