The invention discloses a Chinese medicinal herb additive for improving immunity of juvenile sea cucumber. Astragalus serves as a main raw material, and is added with codonopsis pilosula, eucommia bark, corydalis bungeana, areca seed, tangerine peel, bupleurum, fortune eupatorium herb, ash bark, szechuan lovage rhizome, Chinese gall, baical skullcap root, lightyellow sophora root, garlic, indigowoad leaf, honeysuckle, dutchmanspipe fruit, berberis, rhubarb, beta-glucan, yeast, mannan oligosaccharide and the like to prepare a Chinese medicinal herb feed additive for promoting immunity. The additive has high attraction on sea cucumber, and has the advantages of no pollution, no residue, no medicament resistance, no side effect and the like. When the additive is added into a common feed to feed the sea cucumber, the additive can promote immune cell differentiation, maturity and multiplication of immune tissues of the sea cucumber so as to promote the immunity of the sea cucumber. Therefore, the sea cucumber has high survival rate, high weight increment speed, and the juvenile sea cucumber has fast color change and high extension, and the additive has an obvious effect of protecting the juvenile sea cucumber.