The invention provides a cable force monitoring device for an attached-type stay cable. In the technical scheme of the invention, a reliable composite semi-rigid contact cohesion-type mechanical deformation transmitter is installed at the position of a fixed scale distance on a stay cable with a traditional structure; a temperature self-compensating fiber grating precision strain transducer is adhered to the surface of the stay cable through the composite semi-rigid contact cohesion-type mechanical deformation transmitter; and the axial strain caused by the change of the pulling force applied to the stay cable in a scale distance is measured; the axial strain of the stay cable is converted into optical signals through the fiber grating precision strain transducer, and the optical signals are transmitted to a collecting demodulation terminal through an optical cable for demodulation; and testing software automatically calculates the corresponding cable force variation value according to strain measurement data, stay cable cross section geometric parameters and mechanical property parameters of stay cable materials, and further the automatic real-time dynamic monitoring of the stay cable is realized.