Abstract: To clarify the resistance risk of Sclerotinia sclerotiorum to the succinate dehydrogenase inhibitor (SDHI) fungicide bixafen, the sensitivity of 103 field strains of S. sclerotiorum collected from different regions of oilseed rape fields in Henan Province was determined using the mycelial growth rate method. Eight resistant mutants were obtained through fungicide induction, and their genetic stability, fitness, cross-resistance, target gene sequences, and expression levels were subsequently investigated. The results showed that the mean EC₅₀ value of the 103 S. sclerotiorum strains to bixafen was (0.4369 ± 0.1523) μg/mL, with a unimodal frequency distribution. This mean value could be used as the baseline sensitivity of S. sclerotiorum to bixafen in Henan Province in 2025. Compared with the parental strains, the resistant mutants showed significantly reduced mycelial growth rates, sclerotial production, and pathogenicity. Most resistant mutants exhibited increased sensitivity to abiotic stresses induced by sorbitol, sodium chloride, sodium dodecyl sulfate, and Congo red, whereas some mutants showed reduced sensitivity to hydrogen peroxide stress. Cross-resistance assays showed that bixafen exhibited no cross-resistance with dimethachlon, fludioxonil, or epoxiconazole, but exhibited positive cross-resistance with pydiflumetofen and boscalid. Target gene sequencing revealed no point mutations in any of the Sdh subunits in the eight resistant mutants. Further reverse transcription quantitative PCR (RT-qPCR) analysis showed significant differences in the expression levels of Sdh target genes among the resistant mutants. Compared with the parental strains, the expression levels of all Sdh subunits were significantly increased in mutants X3L-1, X3L-2, and P2L-1, whereas only some Sdh subunits were upregulated in mutants P2L-4 and P2L-5. In addition, no significant changes in the expression levels of any Sdh subunits were observed in X3L-3, P2L-2, or P2L-3, suggesting that their resistance may be primarily mediated by non-target-site mechanisms. This study characterized the sensitivity level and resistance risk of field strains of S. sclerotiorum from oilseed rape fields in Henan Province to bixafen, providing a theoretical basis for the scientific and rational use of this fungicide and for resistance management.