The stay cables in civil engineering are one of the most difficult components to maintain for the safety of bridge after it is open for traffic, as the slenderness ratio is large, and they are flexible, low in damping ratio and less resistant to bending. It is possible that the cable snaps under large cyclic flexural stress due to wind-induced motion, regular traffic or even ambient vibration. The loosening seal of stay cables, damaged anchors, and tendon corrosion due to damaged protection sleeve at the root will undermine dramatically the life of cable-stayed bridge and even its safety. In this paper, the field test used to determine dynamic responses for stayed cable of the bridge in civil engineering. The practice formula is used to determine the cable forces of the Kao Ping Hsi cable-stayed bridge (the largest cable-stayed bridge in Taiwan). The results obtained herein indicate that such analysis is valid and rational, and may be used to monitor the safety of cable-stayed bridge.