To address the difficulty in accurate balancing and calibrating the 2-wire 1/4-bridge strain gauges with long cables, the influence of long cable resistance on the sensitivity of the Wheatstone bridge is analyzed. It is found that the voltage division effect, caused by the long cable resistance being in the same order of magnitude as the strain gauge resistance, induces common-mode offset and leads to uncertain sensitivity. The traditional T-type balancing circuits cannot simultaneously resolve these two issues, a novel 1/4 bridge balancing circuit structure is proposed. By introducing adjustable resistors into adjacent bridge arms, the resistance compensation range of the bridge is expanded, and the uncertain sensitivity problem is solved at the hardware level. On this basis, a self-calibrating strain measurement circuit is designed. Programmable analog switches are utilized to alternate between the calibration and measurement channels, and the voltage of the calibration arm is leveraged to achieve automatic sensitivity calibration. The effects of cable resistance deviations and component tolerances on sensitivity are effectively mitigated. Furthermore, a mathematical model of the improved balancing circuit is established. With the minimization of relative calibration error adopted as the optimization criterion, and the nonlinear relationship between the calibration resistance and the error incorporated, the optimal calibration resistance value is determined. The sources and magnitudes of the system′s sensitivity errors are further analyzed, and the relative error is reduced through methods such as component burn-in and screening. Laboratory tests are conducted on the prototype by simulating various cable lengths and operating temperatures. It is demonstrated by the results that a balancing compensation range of 0～120 Ω for long cable resistance is achieved by the proposed circuit, and a system signal-to-noise ratio (SNR) exceeding 70 dB is obtained. After self-calibration, the sensitivity error is maintained within 1%. In dynamic drop tests of cylinders, an SNR of 70.16 dB for the strain signal is reached, and the effectiveness and dynamic measurement stability of the proposed self-calibrating circuit are fully validated. A valuable reference for the design and engineering application of low-cost, long-cable strain measurement circuits is provided by this solution.