The invention relates to scylla paramamosain soft crab mixed feed and a preparation method thereof. The mixed feed comprises 35-40 parts of fish meal, 25-30 parts of peeled bean pulp, 4-6 parts of shrimp head powder, 4-6 parts of fish dissolved pulp, 10-15 parts of pregelatinized starch, 4-5 parts of fish oil, 0.5-2 parts of soybean lecithin, 0.5-2 parts of cholesterol, 3-4 parts of mixed vitamins, 2-3 parts of mixed minerals, 0.5-1 part of choline chloride, 1-2 parts of monocalcium phosphate, 4-6 parts of sodium alginate and 0.1-0.2 part of eclosion hormones. The mixed feed is particularly designed for scylla paramamosain soft crabs, is balanced in nutrient component, good in palatability and stable in raw material source, and a function of promoting eclosion of scylla paramamosain is achieved after the shrimp head powder, the eclosion hormones as well as the soybean lecithin and the cholesterol of certain ratios are used together; and the LC-PUFA (Long-Chain Polyunsaturated Fatty Acid) of a high ratio, particularly n-3LC-PUFA, is beneficial to increase of the survival rate and the eclosion rate, and nutrition requirements of the scylla paramamosain at specific growth stages can be met; as an adhesive, the sodium alginate is capable of improving the feed water stability and reducing the feed loss rate and can be taken in for 100% by the scylla paramamosain, the culture successrate of 'soft crabs' is 100%, the culture time is shortened by more than 10 days when being compared with that of natural bait or commercial crab feed, and the mixed feed is simple to prepare and very good in popularization value.