The invention discloses a sludge collecting device used for a steam generator of a pressurized water reactor nuclear power plant. A box-shaped structure is included, and comprises a bottom plate, a top plate, and encircling plates connected end to end and arranged between the bottom plate and the top plate; a closed containing space is defined by the bottom plate, the top plate and the encirclingplates; a plurality of steam-water separators are arranged in the containing space; the sludge collecting device further comprises a sludge washing pipeline structure and a sludge collecting pipelinestructure, wherein the sludge washing pipeline structure is arranged on the top plate and communicates with the containing space and is used for washing residues entering the containing space; and thesludge collecting pipeline structure is arranged in the containing space and used for collecting the residues after being washed and discharging the sludge. The sludge collecting device is used for continuously collecting and discharging sludge particles suspended on the secondary side of the steam generator, and therefore deposition of the sludge particles in a pipe bundle area is reduced, the work environment of a heat transfer pipe is improved, and the reliability of the steam generator is improved.