The utility model relates to an evaporative pattern anti-deformation white mold for a large-sized thin-walled valve body; a U-shaped workpiece (6) is bonded with a flange workpiece (7) to form a sealed space (8); a cross rib (5) is arranged in a flange hole of the flange workpiece (7); a first long strip-shaped rib (2) is arranged on the surface of the flange workpiece (7); a second long strip-shaped rib (2) corresponding to the first long strip-shaped rib (2) is arranged on the side surface of the long strip-shaped edge of the U-shaped workpiece (6); a T-shaped rib (4) and an I-shaped rib (1) are arranged in the formed sealed space (8); the I-shaped rib (1) is arranged on a central line of a plane having a distance of 40 mm from the top end; the T-shaped rib (4) is arranged at two ends of the sealed space (8) and symmetric relative to the center; two diagonal braces (3) are arranged above the plane of the T-shaped rib (4); and diagonal lines of the diagonal braces (3) are arranged in the sealed space (8); therefore, deformation of the white mold is effectively overcome, internal and external anti-deformation ribs are removed during cleaning casts, workpiece deformation is avoided and the reject rate is reduced.