With the continuous development of weak magnetic flux leakage detection technology, it has been gradually applied to steel bar stress detection.To further optimize index accuracy and adaptability, a weak magnetic flux leakage characterization parameter method for steel bar stress integrating multiple features was proposed. Experimental data were obtained through steel bar tensile tests. Magnetic characteristic indices were selected and characterized. Index fusion analysis and evaluation were then carried out. The indices derived from the entropy weight fusion method outperform individual indices in linear fitting goodness-of-fit and robustness evaluation. Significant improvements in precision and stability are achieved. A novel approach is provided for enhancing the accuracy and adaptability of detection indices.