A constant-resistance and large deformation anchor cable and a constant-resistance device are provided. The constant-resistance and large deformation anchor cable comprises cables (7), an anchoring device (13), a loading plate (12) and clipping sheets (4). The upper end of cables (7) is fixed on the anchoring device (13) and the loading plate (12) by clipping sheets (4). The constant-resistance and large deformation anchor cable also comprises a constant-resistance device, and the constant-resistance device comprises a sleeve (8) and a constant-resistance body (5). The sleeve (8) is a straight tube. The constant-resistance body is conical, and the diameter of the lower end of the constant-resistance body is bigger than the diameter of the upper end of the constant-resistance body. The inner diameter of the sleeve (8) is smaller than the diameter of the lower end of the constant-resistance body. A cuneiform part is arranged on inner wall of the lower end of the sleeve (8), and the constant-resistance body (5) is arranged on the cuneiform part. The strength of constant-resistance body (5) is higher than the strength of the sleeve (8), thus the sleeve (8) generates plastic deforming and the shape of the constant-resistance body (5) is not changed, when the constant-resistance body (5) moves in the sleeve (8). The lower end of the cables (7) is fixed on the constant-resistance body (5). The constant-resistance and large deformation anchor cable and the constant-resistance device have the properties of constant-resistance and preventing fracture, and can detect and early warn the all process of the activity of the landslides and the causative fault.