Abstract: In order to find the best mechanical transplanting density of rice planted after tobacco, by taking Guang 8 you 165 as the material, the effects of different mechanical transplanting densities on the growth period, agronomic traits, yield and yield components of rice planted after tobacco were studied by using the single factor random block design. The results showed that the maximum yield was 10 152.0 kg·hm^-2 when the mechanical transplanting density was 30 cm×14 cm (treatment D), which was significantly higher than that of 30 cm×21 cm (treatment A), 30 cm×18 cm (treatment B) and 30 cm×12 cm (treatment E). When the mechanical transplanting density was in the range of 158 730-238 050 holes·hm^-2, the number of productive ear per unit area increased significantly with the increase of planting density, and the yield also increased correspondingly, while the number of panicles per hole, the number of grains per panicle, the thousand kernel weight and the setting percentage decreased. If the mechanical transplanting density exceeded a certain range, when being planted too densely, the yield increase would be affected.