The rapid development of flexible electronics has led to an increasing demand for multifunctional flexible sensors. However, the preparation of such sensors is still limited by material and equipment constraints. The aim of this study is to develop a novel method for fabricating high-performance sandwich-type flexible strain sensors using photocuring additive manufacturing technology to address the limitations of current fabrication methods. A flexible conductive composite resin was prepared by the simple mixing of materials. A custom multimaterial digital light processing (DLP) system was used to integrate multiple materials and form the sandwich structure. The mechanical and electrical properties of the resulting sensor were evaluated through a series of experiments. The sensor exhibited a high sensitivity coefficient of 5.355, an impressive deformation capability of up to 105%, and excellent mechanical durability. The strong adhesion between layers and the enhanced mechanical properties of the sandwich structure contributed to its superior performance compared with single-material sensors. Additionally, the sensor was successfully applied to monitor the flight motion of a flapping-wing aircraft, demonstrating its potential for practical applications. This work provides a simplified and efficient method for fabricating flexible sensors and valuable insights for the development of next-generation wearable and flexible electronic devices.