Abstract: This research aims to select and identify tobacco germplasms which have different sensitivities to low temperature in flower bud differentiation. Tobacco recombinant inbred lines LM2 and HM1 are used as materials, and their seedlings are treated under low temperature and room temperature, and then transplanted into field. The growth of meristem is observed dynamically under the stereomicroscope. The results showed that the flower bud differentiation process of LM2 under low temperature treatment was similar to that in the room temperature. The low temperature treatment for LM2 at seedling stage had no effect on the flower bud differentiation process. The floral primordium of LM2 was formed after transplanted into field for 30 days, began differentiating after 35 days, and the small flower primordia were developed after 40 days. However, the flower bud differentiation process of HM1 under low temperature treatment was different from that of the room temperature. Under low temperature treatment, HM1 entered the initiation stage of flower bud differentiation after transplanted for 25 days, got in the inflorescence primordium formation stage in the 35th day, and entered the flower organ development stage in the 40th day. It indicated that the HM1 and LM2 lines were a couple of special germplasm which had differences in low temperature sensitivity, they could be used to analyze the mechanism of flower bud differentiation in responding to low temperature at seedling stage, and breed tobacco variety flowering early and resistant to low temperature.