The invention discloses a clamp-on cable force monitoring device. The clamp-on cable force monitoring device comprises two clamping devices which are sleeved on a to-be-detected cable, and a linear displacement sensor which is fixedly arranged on the clamping devices through connection members and is arranged between the two clamping devices, wherein the linear displacement sensor is used for detecting vertical displacement amount S of the to-be-detected cable, and corresponding cable force F is acquired according to a cable S-F curve. The monitoring device is advantaged in that cable force measurement can be accomplished on the basis of no damage to a rope structure, and hidden safety trouble can be prevented; raw materials are cheap, integral cost is low, a mounting process is simple, the monitoring device is convenient to dismount, multiple times of cycle utilization can be realized, economic performance and environmental protection are realized, test cost is low, test precision is relatively high, cutting or dismounting of the cable can be avoided in an operation process, influence on construction can be avoided, and engineering efficiency is improved.