Aiming at the measurement errors caused by the resistance of high-temperature long wires and their temperature variations in long-distance strain testing of high-temperature structures for nuclear power applications, this paper proposes a strain correction method integrating strain gauge test data, measured strain gauge resistance and wire resistance values. The formation mechanism of strain measurement errors under long-wire transmission conditions is analyzed. By introducing resistance parameters of strain gauges and connecting wires, a unified correction model for measured strain is established to calibrate strain readings acquired at high temperatures. Based on the model, the thermal output curves and gauge factors are determined. High-temperature strain tests at 350 °C were performed to verify the effectiveness of the proposed method, which is further compared with the traditional three-wire method and half-bridge compensation method. The results demonstrate that the proposed method can simultaneously account for the coupled effects of wire resistance and its temperature drift, substantially reduce measurement errors, and improve the accuracy and stability of test results. This work provides critical technical support for enhancing the precision of high-temperature long-wire strain measurement in the nuclear power industry.