The invention relates to the technical field of aquatic feed processing and particularly relates to an aquatic feed and a preparation method thereof. A fish feed is prepared from the following raw materials in parts by weight: 30.17-34.17 parts of rapeseed meal, 15.00-19.00 parts of corn starch, 26.00-30.00 parts of bean pulp, 13.00-17.00 parts of corns, 1.4-1.6 parts of grease, 1 part of a premix, 2 parts of monocalcium phosphate, 1 part of granulesten and 0.20 part of choline. According to research, the feed coefficient of a carp feeding expanded feed is remarkably lower than that of a feeding hard granule group at the same formula condition, and the breed cost of carps can be greatly lowered. After wheat flour is replaced by the corn starch in the feed, the growth performance and the survival rate of the carps are not remarkably influenced, and the cost can be further lowered; and however, the fatness of the carps is increased.