The invention belongs to the technical field of water electrolysis hydrogen manufacturing and discloses a catalyst Co9S8/rGO for water electrolysis hydrogen manufacturing and a preparation method thereof. The molecular formula of the catalyst is Co9S8/rGO, and a Co9S8 nanosheet grows on an rGO nanosheet structurally. The preparation method comprises the following preparation steps that GO is completely dispersed into acetone; a precursor Co(TU)4(NO3)2 is added into acetone dispersion liquid of GO, then stirring is conducted in a water bath at the temperature of 35-40 DEG C till a solvent evaporates, and thus a Co(TU)4(NO3)2/GO composite is prepared; the Co(TU)4(NO3)2/GO composite, organic amine and organic phosphorus are heated up to 190-250 DEG C under protection of the inert atmosphere to be pyrolyzed for 4-12 h and cooled to the indoor temperature, then centrifugal washing treatment is conducted through ethyl alcohol, n-heptane and chloroform, and thus the catalyst Co9S8/rGO is prepared. According to the catalyst Co9S8/rGO for water electrolysis hydrogen manufacturing and the preparation method thereof, the Co9S8/rGO catalyst is prepared by adopting the method that the precursoris pyrolyzed in an organic amine and organic phosphorus system, and the prepared Co9S8/rGO catalyst is used for water electrolysis hydrogen manufacturing and has quite high activity.