The invention provides an open-loop adjustable cable force measuring device and a measuring method thereof. The open-loop adjustable cable force measuring device comprises a detector, a controller, afirst half-loop coil, a second half-loop coil and an open-loop shell; the first half-loop coil is in butt joint with the second half-loop coil, and the two ends of the first half-loop coil and the twoends of the second half-loop coil are overlapped; the open-loop shell covers the surfaces of the first half-loop coil and the second half-loop coil, and the detector is embedded in the first half-loop coil or the second half-loop coil and is in signal connection with the controller. According to the open-loop adjustable cable force measuring device and the measuring method thereof, through setting and adjustment of the butt-joint and overlapping range between the first half-loop coil and the second half-loop coil, the device is suitable for inhaul cables of different specifications, and thusthe flexible open-loop shell is utilized for adaptively locking the inhaul cables; the structure can be applicable to various inhaul cables of different specifications, periodic disassembly, assemblyand replacement can also be achieved, and the accuracy and reliability of the detection result of the measuring device are effectively guaranteed.