In order to understand the cytological mechanism of pollen abortion of genetic male sterile mutant induced by space night in maize, the sister cross population were used for sterility anal． ysis and cytological observation．Intact anther obselvation,isolated cells observation and paraffin sec-tion were adopted in this research．The results strawed that pollen abortion occured mostly in dyad stage of meiosis in genetic male sterile mutant. The dyad were degenerated with abnormal shape. In late aether developing stage,the tapetal cells were giant vacuolated and delayed degeneration．The pollen mother cells(PMC)began to dissolve and degenerate in a few anther before meiosis.