The cable is a key load-bearing component of cable-stayed bridges， and its stress state is an important indicator for assessing the safety of bridge structures. Accurate measurement of cable forces is crucial to ensure the safety of the bridge. Based on this， this paper establishes a set of cable force identification system for cable-stayed bridges that can achieve long-distance， non-target， and high-precision measurements. The system utilizes an improved line segment detector （LSD） to track the cables and identify their vibration information. The valid vibration signals of the cables are then discretely extracted using the variational mode decomposition （VMD） method to obtain their frequency information. Finally， the cable forces are estimated using the vibration frequency method based on the cable’s frequency information. The accuracy and robustness of the improved LSD and the cable force identification system are confirmed through experiments conducted in the laboratory on a model with a large slenderness ratio and low pixel ratio， as well as cable force identification on a large-span cable-stayed bridge. In the laboratory experiment using a steel ruler model， the improved LSD identified the vibration information of the ruler with an error of only 0.63% compared with the laser displacement sensor. In the experiment on a large-span cable-stayed bridge， the error in the identified cable forces by the system compared with the contact sensors was less than 3.0%. Both experiments demonstrate that the proposed system can accurately identify cable forces in complex engineering field environments.