The invention discloses a water-cultured floating seedling method of photinia glomerata. The water-cultured floating seedling method comprises the steps of 1, building a floating seedling pool, including selecting a site, building the pool and putting up a shed, 2, mixing humus soil, perlite, saw dust, laterite and fine sand together in the ratio of 6: 2: 2: 1.7: 0.5, when preparing a matrix, firstly crushing the humus soil and the laterite, and then adding the fine sand and the perlite and mixing evenly, performing sterilization treatment on the mixed matrix (by use of a fumigating method), next, adding 10% of water for even wetting, and finally, regulating the PH value of the matrix to the range of 5.5 to 7.0, 3, putting the matrix in a tray and sowing seeds, 4, selecting nutrient pool water from unpolluted underground water or drinking water having the PH value in the range of 5.5 to 7.0, 5, controlling the temperature and the humidity, namely controlling the temperature in the shed in the range of 15-30 DEG C and the relative humidity in the shed in the appropriate range of 80% to 85%, and 6, replacing the floating seedling nutrient solution of the photinia glomerata and the floating pool water every 30-40 days, and beginning from the second time of water replacement, adding the nutrient solution every time to guarantee nutrition supply to the seedlings.