The invention discloses a multifunctional detection apparatus for spent fuel assemblies, comprising a bellmouth adapter, a bottom plate device, an X-Y shifting platform, a calibrating module for calibrating diameter of peripheral fuel rods and thickness of an oxide film, and a measuring module for measuring the diameter of the peripheral fuel rods and the thickness of the oxide film; the bellmouth adapter is fixed to a bellmouth of a loading lift, the bottom plate device comprises a base plate mounted at the bellmouth adapter and a clamping mechanism mounted on the base plate, the base plate, the bellmouth adapter and the bellmouth are communicated in a lifting direction, the loading lift extracts out a spent fuel assembly or places the same at the communication part of the base plate, bellmouth adapter and bellmouth during lifting, the clamping mechanism is used for fixedly clamping the spent fuel assembly placed, the X-Y shifting platform is mounted on the base plate, the calibrating module is mounted on the base plate, the measuring module is mounted on the X-Y shifting platform, and the X-Y shifting platform drives the measuring module to move positionally in directions X and Y so as to achieve multidirectional detection.