The invention relates to a block sheet preparation assembly and device for corrosion test of weld flux residues. The sheet preparation assembly comprises an extruding piece and a support piece, wherein the extruding piece comprises an extruding part and a forming bulge which is arranged on the extruding part; the support piece comprises a support part and a forming groove which is arranged on thesupport part; the forming bulge is in extrudable matching with the forming groove. The sheet preparation device comprises the sheet preparation assembly, a base body and a drive source, wherein the support piece is arranged on the base body; the drive source is arranged on the base body, the extruding piece is in driving connection with the drive source, and the forming bulge on the extruding piece corresponds to the forming groove on the support piece. The sheet preparation assembly and device have the advantage that by extruding a sheet block on the support piece by the extruding piece, andthe surface of the sheet block forms the groove, the irregular surface of the groove due to nonuniform force applying by a worker is avoided, and the influence to the judgment of the corrosion test results due to damage to the groove surface of the sheet block can be effectively avoided.