The invention belongs to the field of rail traffic, and particularly relates to a secondary casting type prefabricated plate, a floating ballast bed composed of the same and a construction method. Thesecondary casting type prefabricated plate comprises a prefabricated plate body. A rail bearing table for arranging a rail structure is arranged on the prefabricated plate body. At least one end, inthe longitudinal direction, of the rail of the prefabricated plate body is provided with reserved connecting steel ribs. The secondary casting type prefabricated plate is simple in structure and convenient to use, and product size and quality are easier to guarantee; the floating ballast bed using the secondary casting type prefabricated plate is higher in integrity, safety and construction quality and construction efficiency and good in applicability and practicability; the construction method of the floating ballast bed is high in targeted property and easy and convenient to operate and canbe selected to be used when an elastic cushion floating ballast bed, an elastic block floating ballast bed, a lateral mounted type steel spring floating ballast bed or a built-in H-steel spring floating ballast bed or other floating ballast beds of specific forms are constructed according to the difference of elastic vibration isolation devices.