Cutting, splitting and breaking transformation construction method for existing overall ballast bed of subway

The invention discloses a cutting, splitting and breaking transformation construction method for an existing overall ballast bed of a subway. The method includes the steps that the ballast bed is perpendicularly cut on a concrete ballast bed plate in the longitudinal direction of a line within the distance of not larger than 3.6 cm through a wall saw, and cutting is conducted to the depth that the part between a concrete face to steel bars is cut off but a pipe piece is not damaged; then, a coring drilling machine is used for drilling along a cutting line, the number of drill holes is 2-6, the diameter of the drill holes is determined according to requirements, the depth of the holes is determined according to the requirement of a splitting bar, the hydraulic splitting bar is inserted into the drill holes to adjust the splitting direction, and pressurizing expanding is conducted until the plate disengages from a pipe wall; and finally, a cantilever crane in a subway tunnel is used for craning the existing broken plate and conducting construction to newly lay a floating plate, and accordingly the transformation of the existing ballast bed is completed. The method is low in construction cost, easy to operate, high in construction speed and low in noise, construction is not stopped on an operation line, safety and reliability are achieved, and the requirements for urban civilized construction, operation line transportation, operation line safety and construction efficiency are met. The popularization prospects are wide.