Abstract: A practical method of applying torque wrench to prestress the steel wire rope in the flexural strengthening with steel wire rope-polymer mortar composite is proposed.The rule of tension change and the prestress loss mechanism of steel wire rope are studied.The torque coefficient, effective prestress coefficient and prestress loss rate are experimentally obtained.The test results show that the tension torque has a linear relationship with the tension force on the wire rope, and the torque coefficient k was about 0.2192.The prestress loss mainly occurred a short period, about 5 min, after the wire rope was tensioned and anchored, and the value accounted for about 50% of the total prestress loss for 72h.After 7h anchoring, the tension of the wire rope basically remains unchanged, and the effective prestress tends to be stable.Based on the test results, the formulas for calculating the tension, effective prestress coefficient and prestress loss rate of the wire rope under different tensioning moments are put forward.The accuracy of the formula is verified by calculation results and experiments.