The utility model provides a cable wire internal force testing instrument relating to a force measuring instrument applied for measuring the internal force of a cable. The prior art has the defects of great effort during utilization and large measuring error. The utility model is comprised of a heavy frame and a cable clamping assembly that is arranged between two ends of the heavy frame. The utility model is characterized in that the cable clamping assembly is connected with a motive power input axis that can have lifting and dropping movements through a pull force sensor; a motive power input assembly is also comprised and connected with the motive power input axis through a reducer structure; and the motive power input axis is also connected with a deflection sensor. Through improving the cable clamping force feeding structure and the measuring instrument, the measuring precision is improved with a stable work, and the targets of effort-saving and convenient operation are achieved.