Abstract: The paper aims to understand and reveal the stage of pollen abortion and the cytological character sterile of CMS 105A, and prove the basic data for studying the CMS of Brassica napus on the molecule level. Observation of anther in Brassica napus cytoplasmic male sterility line 105A and its restoring line was made by means of paraffin section method in order to determine the time when the anther development was inhibited and the sterile mode. It indicated that: one part of 105A anther development was inhibited at the time of sporogenous cell stage, the other part was inhibited at the stage of uninucleic pollen. The hypertrophic tapetal cells were abnormal enlarged, the disintegrated tapetum cells infiltrated into the location around the pollen mother cells and conglutinated with the pollen mother cells. The tapetum cells disaggregated with protoplasm shrinking and degraded into densely stained mass, they occupied too much space and compressed the microspores and caused the sterility of pollen grains.