Objective To address the difficulty in real-time monitoring of the access sheath posture during Flexible Ureteroscopic Lithotripsy (FURL), this paper proposes a flexible sensor based on graphene nanowalls (GNWs), aiming to achieve high-sensitivity, low-cost, real-time perception of catheter bending angle and direction during surgery. Methods A four-channel flexible conformal angle sensor array integrated at the front end of the access sheath was designed and fabricated. The strain distribution characteristics of the sensor under different irrigation flow rates and bending angles were systematically investigated through fluid-structure interaction finite element simulation. A mechanical-electrical test platform was established to experimentally validate the sensor's sensitivity, repeatability, hysteresis, drift, and cyclic durability. Results Simulation results indicated a strong linear relationship between sensor strain and bending angle, and the influence of irrigation flow rate on angle measurement was negligible. Experimental results showed that the sensor exhibited stable response and high repeatability within a 0~180° bending range, with no significant performance degradation after 2000 cycles. Bending direction and angle could be accurately identified via the four-channel resistance changes and their vector synthesis. Conclusions The developed flexible conformal sensor system can effectively monitor the posture of the ureteroscopic access sheath. It features high sensitivity, good stability, and strong robustness, providing a feasible technical solution for real-time intraoperative catheter posture feedback. This system holds promise for enhancing surgical safety and stone clearance efficiency.