To address the steering performance loss resulting from the inability to maintain preset magnitude and direction of guiding force due to single-wing-rib failure in directional drilling tools, a steering performance optimization model was developed for single-rib failure scenarios. A periodic guiding force-borehole trajectory model was established, along with trajectory calculation method under unsteady guiding forces. A minimization model of trajectory endpoint deviation within sleeve rotation cycles was developed, accompanied by a guiding performance evaluation criterion for unsteady guiding conditions. An improved sparrow search algorithm(ISSA) dynamically adjusted thrusts of functional ribs, effectively enhanced guiding force efficiency and minimizied trajectory deviations during sleeve rotation cycles. Results show that the model essentially eliminates trajectory deviations and fully restores steering performance under trip-free conditions when the guiding force is ≤50% of the maximum value. Beyond this threshold, it still significantly mitigates performance loss, but the mitigation effect gradually diminishes with increasing guiding force. This optimization model effectively reduces the steering performance loss of drilling tools under single-wing-rib failure conditions and demonstrates significant engineering application value.