The invention provides a carbonate fracture cavity inner structure acquiring method and device. The method comprises steps: a bead-like seismic phase outside the carbonate fracture cavity is acquiredthrough a predetermined feature; a porosity threshold of a target layer inside the carbonate fracture cavity is acquired; the seismic data are processed through a seismic inversion technique to obtaina porosity data volume of a cavernous reservoir inside the carbonate fracture cavity and a porosity data volume of a pore-type reservoir; a porosity data volume of a fractured reservoir inside the carbonate fracture cavity is acquired through the seismic data; and according to the bead-like seismic phase outside the carbonate fracture cavity, the porosity threshold of the target layer inside thecarbonate fracture cavity, the porosity data volume of the cavernous reservoir, the porosity data volume of the pore-type reservoir and the porosity data volume of the fractured reservoir, the spatialstructure of the fracture cavity is determined. According to the carbonate fracture cavity inner structure acquiring method and the device provided in the invention, the spatial structure of the fracture cavity can be acquired.