Promoting the detection range, durability, and shapeable manufacturing of flexible strain sensors is essential to broaden their applications. Therefore, in this study, styrene ethylene butylene styrene (SEBS) rubber as a flexible material and a melt-mixing molding method are adopted to design an ultra-flexible strain sensor. Carbon nanotubes (CNTs) are added to form a conductive network, and the effect of Ag flakes on improving the sensor performance is studied. The experiment results exhibit good strain-resistance dependent characteristics of the obtained sensor, which demonstrates an excellent sensing range of about 540% with a gauge factor (GF) of 5.197. The good hydrophobicity (water contact angle ≈120.4°), repeatable characteristics at different rates, strain-dependence and long-term recycling of the sensor are demonstrated as well. Finally, the fabricated round bracelet sensor is applied to detect different cross-sections, the movement of human joints, balloon inflation, bottle cap sealing and numerous other aspects.