The invention relates to a ballast bed base prefabricated slab and an application thereof. The ballast bed base prefabricated slab comprises a slab body formed by prefabricating reinforced concrete materials. The size of the slab body is smaller than the design size of a base. At least three height and dip angle adjusting devices are arranged on the slab body. The ballast bed base prefabricated slab is simple in structure, capable of being processed and manufactured in the place outside a tunnel or a factory, and the processing precision and quality are more easily ensured. The ballast bed base constructed by applying the ballast bed base prefabricated slab is small in error and high in precision. The construction method for the ballast bed base constructed by applying the ballast bed base prefabricated slab is easy, convenient and rapid to operate, the flatness, cross fall and other key indexes of the base can be effectively controlled with the help of the ballast bed base prefabricated slab, the site construction difficulty is greatly reduced, the construction efficiency can be greatly improved, waste caused by secondary treating or reworking is reduced, the ballast bed base prefabricated slab is excellent in economical performance, practicability and applicability and can be widely used for base construction inside the tunnel with linear segments and curving segments, and market application prospects are quite wide.