A constant-resistance large-deformation anchor rod includes a rod body (6), a tray (3), a nut (2), and a constant-resistance device (4). The constant-resistance device (4) is formed into a cylindrical structure, and the inner surface of the constant-resistance device (4) and the outer surface of the rod body (6) are both formed with thread structures. The constant-resistance device (4) is sleeved at the tail of the rod body (6), and the tray (3) and the nut (2) are sequentially sleeved at the tail of the constant-resistance device (4). The nut (2) is in threaded connection with the constant-resistance device (4). The constant-resistance large-deformation anchor rod in the invention can be automatically stretched when the tunnel surrounding rock deforms largely, and keep the constant working resistance.