The invention provides a roadway bottom plate supporting structure and a construction method of the roadway bottom plate supporting structure. A grouting reinforcement layer is arranged below a roadway bottom plate. A plurality of pressure relief holes are formed in the grouting reinforcement layer. An anchoring body is arranged below the pressure relief holes. Anchor ropes are fixed to the anchoring body. The anchor ropes penetrate through a plurality of cover plates and are connected to a steel beam used for pressing against the cover plates. The steel beam is provided with a lock used for tensioning the anchor rope. According to the roadway bottom plate supporting structure and the construction method of the roadway bottom plate supporting structure, the pressure relief holes reserve deformation space for deformation of the roadway bottom plate, as a result, stress of the roadway bottom plate is transferred deep, and maintenance of a shallow stratum of the roadway bottom plate is promoted; meanwhile, the anchoring body is located on a deep stratum portion with high stability, the grouting reinforcement layer which is formed by shallow surrounding rocks and the anchoring body are connected into a whole through the anchor ropes, and therefore deformation of the shallow surrounding rocks of the roadway bottom plate is restrained effectively. Besides, the pressure relief holes and the anchor ropes are connected integrally to form the overall supporting structure, so that the roadway bottom plate supporting structure is more stable.