The invention discloses waterproof phosphogypsum plastering mortar dry powder. The dry powder comprises the following components in parts by weight: 20-29 parts of phosphogypsum base gelatinization material, 68-77 parts of sand, 0.5-3.0 parts of waterproof agent, 0.2-1.0 part of retarder and 1.5-5.0 parts of water-retaining agent. The phosphogypsum is used for preparing waterproof plastering mortar dry powder, a new technological method is provided for solving the problems of occupation space, environmental risks, potential safety hazards and the like of the industrial waste phosphogypsum, moreover, local resources are used, the utilization of a local material-superfine sand is solved, on the one hand, environmental load is reduced and the positive cycle of the gypsum industry is promoted, and on the other hand, the cost of gypsum plastering mortar is also lowered. In addition, compared with the waterproofness of the conventional gypsum-based material, the waterproofness of the gypsum plastering mortar which can be produced through the phosphogypsum plastering mortar dry powder and has the softening coefficient of 0.86 is obvious.