In wheat (Triticum aestivum L.), S-type cytoplasmic male sterile (S-CMS) lines can mainly transform from sterility to fertility at the mononuclear pollen stage. Observations from microscopy revealed an inhibition of starch accumulation within the pollen grain, suggesting that an alteration in carbohydrate metabolism or assimilate supply may be involved in S-CMS pollen abortion. We measured levels of various carbohydrates and activities of key enzymes of sucrose metabolism at the mononuclear pollen stage in anthers collected from an S-CMS line and its maintainer line and found that nonreducing sugars increased in S-CMS anthers. Sucrose accounted for part of the nonreducing sugar accumulation. The activity of invertase declined significantly, whereas sucrose synthase activity during starch accumulation in pollen showed no significant change in S-CMS anthers at the mononuclear pollen stage. The results suggest that sucrose conversion and inhibition of invertase were probably responsible for the pollen abortion. Because there is a high correlation between the rate of ethylene evolution and sucrose content, ethylene anabolism was determined. TaACS2 regulates sucrose metabolism in pollen probably through catalysing the synthesis of ethylene precursor 1-aminocyclopropane-1-carboxylic acid in wheat. In this study, ethylene production of anthers underwent accumulation, revealed by gas chromatography, and expression levels of TaACS2 were upregulated in the S-CMS line, as determined by quantitative real-time PCR. We investigated the DNA methylation pattern of TaACS2 in the core promoter region using bisulfite genomic sequencing, and lower methylation was observed in the S-CMS line. These results suggest that DNA methylation of the TaACS2 gene may be involved in the sterility–fertility transition by regulating the synthesis of ethylene in S-CMS anthers.