Using the thermo-sensitive genic male sterile(TGMS) Brassica napus line W21 as the experimental material, this study systematically investigated the critical period, characteristics, and inheritance pattern of pollen abortion by combining morphological observation, genetic analysis, and cytological examination. The results showed that the critical fertility transition temperature of W21 was 22 ℃. Under 18 ℃, the plants exhibited complete male fertility, with normal stamen development, bright yellow anthers, and plump pollen grains. In contrast, when the temperature exceeded 22 ℃, anther degeneration occurred, leading to sterility. The sterility trait of W21 was controlled by at least two pairs of recessive nuclear genes. The pollen abortion process of W21 initiated at the pollen mother cell stage and culminated in complete abortion during the middle-late uninucleate stage. The key cytological characteristics of abortion include: abnormal development of the anther epidermal structure; premature degeneration of the tapetum accompanied by abnormal vacuolization; formation of abnormal tetrads due to meiotic irregularities in pollen mother cells; and defects in pollen exine development. These abnormalities ultimately resulted in microspore adhesion and cytoplasmic degradation, leading to complete pollen abortion.