The invention discloses a preparation method of a sodium alginate fiber for surgical dressing, and belongs to the technical field of sodium alginate fiber preparation. The method includes steps of taking fresh kelp as raw materials, immersing the kelp by sodium hydroxide solution after chopping; making the internal fiber of the kelp swell; instantly releasing pressure after heating and preserving pressure, and making the kelp cell tissue break; performing ultrasonic treatment after adjusting pH value by hydrochloric acid; further releasing effective components through cavatition of ultrasound wave; adding calcium chloride to make it settle after ion exchange reaction; after dissolving the sediment by sodium chloride solution, using ethanol as the precipitator; refining the effective components; after filtering and drying, co-mixing and modifying with wheat vital gluten and peach gum at ratio; at last, acquiring the sodium alginate fiber for surgical dressing through spinning, freezing and drying. Through the co-mixing and modification of the high-purity sodium alginate, vital gluten and others, the method improves the flexibility of the sodium alginate fiber, improves the elongation at break, and widens the using scale of the sodium alginate fiber.