Preparation method of feed additive serine

The invention provides a preparation method of feed additive serine, comprising the steps of S1, adding methyl alpha-bromo-beta-methoxypropionate and sodium azide into formaldehyde solution having weight fraction of 20-25%, and holding the temperature at 80-85 DEG C for 1.5-2 hours to obtain a first product containing methyl alpha-bromo-beta-methoxypropionate; S2, subjecting the first product to catalytic reduction and the reduced product to acid hydrolysis, filtering to obtain a second product; S3, adding an extracting liquid into the second product, extracting, and using an aqueous layer as a third product, wherein the extracting liquid ethyl ether; S4, evaporating the third product, washing, and drying to obtain the serine. The method according to the technical scheme of the embodiment acquires a product through the above reaction process, the product having a ratio of serine to isoserine being about 1:(0.6-1.5), with few byproducts produced and normal growth and development animals unaffected; the serine