The invention discloses an internal cleaning device for hydraulic valve block machining and a cleaning method thereof, and relates to the technical field of hydraulic valve block cleaning. The internal cleaning device comprises a circular through groove plate, and a double-shaft motor is fixedly connected with the middle of the right side of the top of the circular through groove plate through a connecting block. According to the internal cleaning device for hydraulic valve block machining and the cleaning method thereof, the double-shaft motor provides power support, a bucket-shaped filter screen body, a stabilizing plate, a telescopic transverse body, a telescopic water pipe, a hollow through net body, a water pump, a water tank box, a slag separation structure, a slag separation net plate, an eccentric wheel rod, a lower conveying belt, a water pumping bent pipe, a water drainage main pipe, a hose, a bent water pipe, a water spraying body, a bevel gear, a bevel gear rod and a conveying connecting belt are used, so that the hydraulic valve block is conveniently and comprehensively cleaned; and meanwhile, residues are removed in time, a telescopic adjusting seat, a bidirectional telescopic plate and a clamping block body are used for conveniently fixing the hydraulic valve block, and a drying box, a fan body, an upper conveying belt, a heating plate and a bearing net plate are used for conveniently drying the cleaned hydraulic valve block.