Abstract: In tethered unmanned aerial vehicles (UAVs), variations in cable slack-taut can generate impact tension, potentially causing cable breakage and uncontrolled UAV crashes, necessitating urgent experimental investigation into this impact tension phenomenon. To this end, this study carries out impact tension experiments for tethered UAV systems in a wind tunnel and analyzes dynamic response data under various structural and environmental parameters to reveal the variation patterns of system's impact tension. Based on the measurement properties of fiber Bragg grating (FBG) sensor, which can be stretched and compressed, criterions are proposed for determining cable slack-taut. Through analyzing the slack-taut distribution with position, it is observed that the slack-taut reduces or disappears with the cable length or diameter decreases, or with the wind speed increases. Experiments on the effects of cable length, diameter, and environmental wind speed on impact tension showed that greater values of each parameter correspond to increase cable tension. Moreover, it is discovered that the tension at the cable-UAV connection point is significant, which affects the UAV's stable motion, hindering normal operation and safe flight. On the premise of practical application requirements, the aforementioned research results suggest selecting a cable with lower length or diameter or higher tensile strength, it is also recommended to prioritize protecting the cable-UAV connection point in structural design, to guarantee stable and safe operation of the tethered UAV system.