The invention discloses a preparation method for a yellow high-strength-and-ductility anti-corrosion AZ91 magnesium alloy block. The preparation method comprises the steps that A, an as-cast AZ91 magnesium alloy is cut into block-shaped test pieces to be subjected to continuous multi-pass equal channel angular extrusion machining, and ultra-fine grain test pieces are obtained; and B, the ultra-fine grain test pieces are cut into the needed shape, the surfaces of the test pieces are cleaned, the micro-arc oxidation reaction is conducted with the test pieces serving as anodes and stainless steel plates serving as cathodes, and according to the proportion, an electrolyte comprises 8-12 g/L sodium silicate, 6-10 g/L potassium hydroxide, 8-12 g/L potassium fluoride, 1-3 g/L staining salt potassium permanganate and sodium citrate, wherein the sodium citrate and the potassium permanganate are added according to the molar ratio of the sodium citrate to the potassium permanganate being 1:1. According to the preparation method, the sodium citrate is adopted to serve as a complex of the staining salt potassium permanganate, the stability of the potassium permanganate can be effectively improved, the film layer staining effect is promoted, the hole diameter and the porosity factor of a manufactured film layer are small, the defects such as holes and cracks do not occur, a large, thick and solid stacking area appears on the surface of the film layer, the compactness of the film layer is greatly promoted, and the anti-corrosion property is good.