In order to study impacts of planting density of mechanical-transplanting rice on lodging resistance and yield, a field experiment was conducted using Indica-Japonica hybrid rice Yongyou 2640, Yongyou 1640 and Indica hybrid rice Fengliangyouxiang 1, Xinliangyou 6380 with six planting densities (A: 31.7 cm × 30 cm, B: 22.2 cm × 30.0 cm, C: 17.1 cm × 30.0 cm, D: 13.9 cm × 30.0 cm, E: 11.7 cm × 30.0 cm, F: 10.6 cm × 30.0 cm). The experimental results were as follows. With the increasing of transplanting density, the yield increased firstly and decreased then, with the highest yield at 13.9 cm × 30.0 cm, both for Indica-Japonica hybrid rice and Indica hybrid rice. The effects of densities on the two types of varieties were not entirely consistent. Under the densities of C–E, the yield of indica-japonica hybrid rice was higher than 10.5 t ha-1, and little or no lodging occurred. Therefore, we could obtain high and stable yield. Under the density of D, the yield of indica hybrid rice was higher than 10.0 t ha-1, and the apparent lodging rate was also higher, so it was difficult to obtain stable yield. With the increasing of transplanting densities, lodging index of two types of rice increased, and stem diameter, wall thickness of culm and dry weight of a unit internode in two types of rice decreased. With increasing filling time, lodging index of indica-japonica hybrid rice increased firstly and decreased then, with the peak value at 30 days after heading, wall thickness of stem, plumpness of internode and single stem weight decreased firstly and increased then, with a minimum value at 30 days after heading. Lodging index of indica hybrid rice was increasing, stem wall thickness was decreasing, plumpness of internode decreased firstly then decreased or increased slightly at 30 days after heading, but not obvious, single stem weight decreased firstly and increased then, with a minimum value at 30 days after heading. The sensitive period of lodging was around 30 days after heading.