The invention provides a sea -flavor potato full-powder low-sugar biscuit, and the raw materials, in quality portion, comprise 30-50 portions of potato full-powder, 10-20 portions of wheat weak gluten flour, 5-10 portions of cream, 3-6 portions of milk powder, 2-4 portions of protein liquid, 5-10 portions of seafood meat emulsion, 1-3 portions of salt, 0.2-1 portion of sodium bicarbonate, 0.2-0.5 portion of ammonium bicarbonate, 10-15 portions of edible oil, 10-15 portions of alga juice, and 30-50 portions of water. The invention also provides a method for preparing the sea -flavor potato full-powder low-sugar biscuit, and the method comprises the steps of modulating a mixed liquor, modulating a dough, making biscuit blanks, and baking the biscuits. According to the invention, the biscuit takes the potato full-powder as the main raw material and has no cane sugar, therefore, the glycemic index is low and the biscuit is suitable for the diabetes; the prepared biscuit has an obvious sea flavor, which covers the special flavor of the potato, therefore, the biscuit can be easily accepted by the consumers; the biscuit has a higher protein content and a higher nutrition value.