In order to illuminate cytological mechanism of small amount 2n pollen existing in petunia, high sterile rate of petunia pollen in hot summer and explore chromosomal karyotype analysis in meiosis period, we conducted the observation of abnormal meiosis and karyotype analysis in meiosis diakinesis period by conventional plate method using flower buds of diploid petunia plant in hot summer as material. The results showed that abnormal meiosis was mainly characterized by multinucleolus, bivalent and sister chromatids dividing beforehand, chromosomes outside metaphase plate, unequal segregation, lagged chromosomes, lost chromosomes, triad and tetrad with micronucleus. These abnormal meiosis behaviour could cause the production of abortive pollen. In metaphase Ⅱ, fusing spindles, tripolar spindle in which spindle were orientated abnormally could easily lead to 2n pollen formation, the occurrence of 2n pollen percentage was 1.51% through statistics. The karyotype formula of Petunia hybrida Vilm. in meiosis diakinesie was K(2n)=2x=14=10m+4sm(SAT), which had 5 pairs of metacentric chromosomes (chrom. No.1,4,5,6,7), 2 pairs of submetacentric chromosomes(chrom. No.2 and 3, No.2 with satellite). Relative length was 2n=14=4M₁+10M₂, belonging to 2A type. The abnormal meiosis of P. hybrida could lead to the production of 2n pollen and sterile pollen, the advantages of karyotype analysis in diakinesis for petunia included abundant materials, clear bivalents form and without artificial pairing analysis, etc al. It provided a new method for study on petunia cytology.