In recent years, paper-based bending strain (PBS) sensors for bending deformation and angle detections have attracted much attention in flexible electronics. However, PBS sensors based on a surface microcrack sensing mechanism have drawbacks of small response and poor water resistance. Herein, we construct a cross-section interface between two conductive papers to form a PBS sensor that can be encapsulated using adhesive tape. Benefiting from the cross-section interface response mechanism of the PBS sensor, it can be directly encapsulated with polyimide tape without worrying about the destruction of the paper surface microstructure. Therefore, the PBS sensor shows excellent water resistance. Meanwhile, the proposed PBS sensor has good bending strain properties. Taking the bending angle of 35.7° as an example, the PBS sensor has a very high response (36.5, relative current ratio after and before bending), good repeatability (2000 times) and acceptable response/recovery times (0.34/0.35 s). In addition, the potential applications of the PBS sensor in the human body and security doors are confirmed. This work not only proposes a novel, high-response, waterproof, and low-cost PBS sensor, but also provides new strategies for the development of bending strain sensors from cross-section interfaces with surface encapsulation.