Abstract: Abstract: Mechanical transplanted rice had many advantages, such as stabilizing yield, saving cost, maintaining high efficiency and freeing labor, and its area was larger and larger in China in recent years. It was reported that the existing row-spacing of mechanical transplanted rice was too big in some rice cultivars with small panicle. Therefore, three panicle types of rice cultivars including large panicle type (LPT include yongyou 2640 and yongyou 8) and medium panicle type (MPT include wuyunjing 24, ningjing 3) and small panicle type (SPT include huaidao 5, huaidao 10) were grown in the field in 2011 and 2012 to investigate the reasonable row-plant spacing of each type of cultivars, the characteristics of dry matter production and the rules of yield formation in mechanical transplanted rice. And the effect of row-plant spacing on grain yield and yield components, leaf area index (LAI), photosynthetic potential (PP), dry matter production and accumulation, crop growth rate (CGR) and net assimilation rate (NAR) were all studied. Results showed that with 30cm row-spacing and expanded plant spacing, it is easy for LPT to obtain high yield due to the larger size of panicle. For MPT, There was no significant difference in grain yield between RS30 (row-spacing of 30cm in mechanical transplanted japonica rice) and RS25 (row-spacing of 25 cm in mechanical transplanted japonica rice), but RS30 had higher yield potential because of well wind and light conditions which may improve filled-grain percentage and 1000-grain weight. For SPT, RS25 was conductive to increase the basic seedlings, and with stable spikelets per panicle, it will obtain high yield because of the significant increase of panicles per unit area. With plant-spacing increased, panicles per unite area of different varieties decreased while spikelets per panicle increased significantly. The filled-grain percentage and 1000-grain weight of RS30 were all higher than that of RS25. With RS30, LPT had higher LAI at heading and maturity, larger spikelet per cm2 leaf area, lower decreasing rate of leaf area, higher dry matter accumulation and PP, CGR, NAR at the medium and late growth period. For MPT, dry matter accumulation of RS30 was fewer than that of RS25, but there were no differences in LAI, PP and NAR between RS30 and RS25. For SPT, because of the larger number of basic seedlings, the LAI at all period stages, PP, CGR and NAR at the medium and late growth period, as well as the amount of dry matter accumulation of RS25 were all higher than that of RS30. Therefore, we concluded that the proper row spacing for LPT and MPT is 30 cm while for SPT is 25 cm. And the japonica rice transplanted by mechanism will realize its yield potential only when different panicle types of rice cultivars match suitable plant-spacing.