The meiosis process and pollen vitality of Longiflorum×Asiatic hybrid ‘Bonsoir’ (2n=3x=36) were studied by cytogenetic methods. The results showed that 64.31% pollen grains were viable，and sizes of the viable pollen grains ranged from 986.33 to 3 491.68 μm2,with a bimodal frequency distribution. During meiosis, some phenomena resulted in sterile pollen grains, such as the irregular chromosome associations in meiosis prophase, lagging chromosomes, chromosome bridges, unbalanced segregation, micronucleus, etc. Abnormal orientation of metaphase Ⅱ spindles contributed to production of dyads and triads, which produced unreduced microspores，such as fused spindles and triangle spindles. But parallel and vertical orientation of spindles was not connected with dyad formation. Concerning the cytokinesis, in some pollen mother cells（PMCs）, a failure of the reductional wall led to monads, dyads and triads, and finally increased the rate of unreduced pollens. The perspective of this allotriploid in the polyploidy breeding program of Lilium was discussed.