Abstract: In order to cultivate blanket rapeseed seedlings suitable for mechanized transplanting, the effects of seed soaking with different concentrations of uniconazole and seedling densities on seedling quality, plant traits in mature period and yield were investigated using‘Ningza 31’as the material. The rapeseed was treated with 0(CK), 5, 10, 15, 20 mg/L uniconazole solution for 2 hours. After natural dry, seedling density was set as 1.5 million, 2.25 million, 3.0 million, 3.75 million and 4.5 million plant/hm2. The results showed that after the treatment of uniconazole, the height of rape seedling decreased, the number of leaves increased, the collar coarsened, root vitality increased, hypocotyledonary axis shortened, overground dry weight decreased, underground dry weight increased, which was benefit to the cultivation of short and strong sprout; with the increase of seedling density, the height of rape seedling increased, the number of leaves decreased, the collar decreased, root vitality decreased, hypocotyledonary axis extended, overground and underground part dry weight decreased, the quality of blanket- seedling decreased; however, with the increase of uniconazole concentration, the influence of seedling density on seedling was significantly decreased. Uniconazole concentration and seedling density had no significant effect on plant height in mature period, total leaf number and main stem length under the blanket-seedling density of 12 thousand plant/hm2, but after the treatment of uniconazole, fruit number of per plant, 1000 seeds weight and harvest yield increased, the treatment of 15 mg/L got the highest yield, and those of 10 mg/L and 20 mg/L were overall equal. With the increase of seedling density, all the economic indicators decreased. According to cropping arrangement, when the needed seedling age was 30 days, the seedling density could reach 4.5 million plant/hm2 under the seed soaking concentration of 10 mg/L, when the needed seedling age was 40 days, the seed soaking concentration could be increased to 20 mg/L, and the seedling density should be ≤3.0 million plant/hm2. By adjusting the concentration of soaking uniconazole and seedling density, blanket seedlings could be cultivated for machine transplanting to meet different rotation systems, and achieve industrialized breeding and echanized transplanting.