According to the design and construction requirements of Puli Tunnel and Ailan Exchange Road in Nantou Section of Taiwan National Highway No. 6 C608 standard (hereinafter referred to as Taiwan C608 cable-stayed Bridge), a new construction method of OVM250 parallel strand cable cable single cable change is introduced in this paper It is to replace the entire unbonded steel strand that needs to be replaced (together with the PE sheath). When the steel strand in the unbonded steel strand is extracted in the process of steel strand replacement, the new steel strand is also brought into the original unbonded PE sheath, and the original unbonded PE sheath is still retained, which greatly simplifies the steel strand replacement process.