<p>Compared to rigid sensors, flexible strain sensors offer promising applications in wearable electronics, human–machine interaction, and health monitoring due to their excellent flexibility, stretchability, and sensitivity. However, achieving both high sensitivity and a wide detection range simultaneously remains a significant challenge. In this paper, we introduce a gap structure based on traditional flexible strain sensors and fabricate a tri-layer composite functional layer using carbon black (CB), graphene (Gr), and conductive carbon paste (CCP) to overcome this challenge. The gap structure effectively concentrates stress at the gap, accelerating crack formation in the flexible strain sensor during stretching. The three-layer gap structure is composed of CB/Gr ink-CCP-CB/Gr ink respectively. The combination of a gap structure and a three-layer composite functional layer enables the sensor to achieve a strain detection range of 70% with good linearity (R² = 0.985) and high sensitivity (GF = 2561). It can also detect small strains as low as 1% (400&#xa0;μm). Furthermore, the sensor exhibits excellent durability in cyclic testing, withstanding over 5000 stretch-release cycles while maintaining a rapid response time of 220&#xa0;ms before and after cycling. This shows that the combination of the gap structure and the three-layer composite function allows the wide detection range, high sensitivity, excellent durability cycle stability, and low strain detection ability to concentrate on the same sensor. The outstanding performance of this flexible strain sensor provides new possibilities for future applications in flexible sensor fields, such as wearable electronics, human–machine interaction, and health monitoring.</p>