The invention provides a preparation method of a biocompatible feather keratin-grafted alginic acid sponge dressing. The method comprises the steps that feather keratin and sodium alginate are taken as raw materials, and feather keratin is pretreated and then grafted to sodium alginate; a condensing agent, a plasticizer and an inorganic cross-linking agent are added, after reacting is conducted for a period of time, dialyzing is conducted with distilled water under the dark condition, freeze drying is conducted, and then the feather keratin-grafted alginic acid feather keratin-based biological external application material is obtained. The sponge dressing has a multi-stage laminated microporous structure, is soft in texture and can quickly absorb water to be swelled and absorb wound exudates to keep the breathability of a wound surface; the absorbing capacity of the sponge dressing has the salt sensitivity, and the sponge dressing can achieve the slow releasing effect on micromolecular drugs, has the certain bacteriostatic property, can be applied to repairing of multiple types of skin wounds such as burns and mechanical injuries and is expected to be applied to the medicine field by serving as a novel functionalized biological external application material.