This paper studies the factors that affect the safe full heading of machine-transplanted rice seedlings in the temperate and cool rice-growing areas, and explores the influence of machine-transplanted rice seedling varieties, seedling age, nitrogen fertilizer application rate and management on the safe full heading of machine-transplanted rice seedlings. Results show that for the mechanized production in the temperate and cool rice-growing areas, we should select the mid-early maturity cold-resistant varieties with growth period of not exceeding 180 d, control the seedling age to be 30-35 d and total amount of pure nitrogen to be not more than 300 kg/ha, and moderately reduce the nitrogen fertilizer postponing ratio. Under this condition, we can achieve safe full heading of machine-transplanted rice seedlings and ensure the yield.