Abstract: In order to reveal the microspore abortive period of Allium cepa cytoplasmic male sterile lines, the microspore development of Allium cepa cytoplasmic male sterile line 8A and its maintainer line 8B was observed and compared by using paraffin section technology. Paraffin section results showed that there was no obvious difference between the growth and development of the microspore in the Allium cepa cytoplasmic male sterile line 8A and its maintainer line 8B during the sporogenous tissue stage. The anther tapetum of the Allium cepa sterile lines 8A completely separated with middle layer cells in pollen mother cell stage, and gradually expanded and extruded pollen mother cells, and then gradually degraded. The residue of degradation invaded into the anther chamber, and mixed together with microspore and adhered to it, and occupied part of the anther chamber and could not supply the nutrients needed for microspore growth, finally microspore degraded, anthers were abortive. This article makes clear that the microspore abortive period of Allium cepa cytoplasmic male sterile line 8A is in the pollen mother cell stage. Therefore, the pollen mother cell stage should be mainly studied in the sterility mechanism study of Allium cepa cytoplasmic male sterile line 8A.