Objective: Design and evaluate a miniature triaxial fiber optic sensor which is integrated into the confined space at the tip of a flexible ureteroscope to measure the contact force during ureteroscopy. Methods: A notched flexure of multilayer continuous beams is deliberately designed to modulate the sensor sensitivity to axial stiffness but not to lateral bending and torsion, and to avoid the crosstalk between axial and lateral forces. Its structure parameters are optimized by the finite element method to meet the needs of miniaturization and performance. A linear decoupled model based on the singular value decomposition algorithm is proposed to accurately compute the forces from the wavelength shifts of fiber Bragg grating. Results: Experimental results show that in the axial direction the sensor has a range of 0-4 N with a resolution of 0.014 N, and in the lateral direction it has a resolution of 0.011 N within the range of -2 N to 2 N, and is able to provide accurate measurement with an error of less than 2%. Conclusion: Primary tests show the excellent competence of the sensor to measure the interactive force at the ureteroscope tip and to discriminate objects, validating its reliability and robustness.