To expand the application of fiber Bragg grating sensors in the field of robotic intelligent sensing， we have designed a novel FBG forearm sensing sheath. In this workstudy， a wavelength -electric conversion control system and the an algorithm forof human-computer bionic tracing were developed. There were three FBG sensing units including tension rings in the forearm sensing sheath. The tension rings made of spandex polyurethane fibers exerted a pre-tightening force on FBGs， which could effectively avoid the traction direction deviation caused by clothing or skin gathering. The joint movements caused the spandex polyurethane fibers to drive the FBGs stretch or axial contractionng axially and the wavelengths shift of FBGs' wavelengths shift. Thereafter， the wavelength-electric conversion control system transfered the motion posture features of human elbow bending angle α， wrist pitching angle β， and knuckle joint motion angle γ to the robot arm's direction θ， height φ， and mechanical claw opening and closing angle ψ， respectively. By deducing the relationship between the range of the human joint movement's range and the output range of the robot arm， the detection coefficient and the control coefficient were obtained. Then， the wavelength-electric conversion coefficient was deduced by converting the dynamic wavelength to the control electric signal in real-time. The experimental results demonstrate that this wavelength -electric conversion control system can make the robotic arm trace the human elbow bending， wrist pitching， and finger joint motion with good linear responses. Within the experimental range， the maximum cumulative error of wavelength-electric conversion coefficient of direction， height， and open/close control output are 0.771 11%，1.992 91%， and 0.341 17%， and the deviation of three control angle outputs are 1.135 60°， 1.720 56°， and 1.826 57°， respectively. The wavelength -electric conversion control system has good control accuracy and it can make the robotic arm track human forearm movements . The research results can provide a theoretical basis to further develop the FBG sensing system of bionic tracing for the robotic arm.