The invention relates to an interest 
protein preparation method and a purpose of the interest 
protein preparation method. The interest 
protein preparation method comprises the steps of obtaining interest protein 
nucleotide sequence fragments, constructing interest protein 
recombinant expression vectors, expressing interest protein in an inducible mode, purifying the interest protein and 
cutting purified products. The fronts of the interest protein 
nucleotide sequence fragments are inserted into 
monomer cutting recognition sites. Preferably, the upper streams of the interest protein 
nucleotide sequence fragments are introduced into kex2 
enzyme cutting sites, and the down streams of the interest protein nucleotide sequence fragments are introduced into 
hydroxylamine hydrochloride enzyme cutting sites. The interest protein is obtained through sequence of event (SOE) technology, and is introduced into 
monomer cutting recognition sites through primers. The interest protein can be human nerve growth factors such as 
thymosin, tiger stripe 
pancreatic polypeptide and tiger stripe 
analgesic peptide. By adopting the interest protein preparation method, obtained interest protein is high in expression quality and easy to purify. Genetic expression products are interest protein 
monomer, no extra 
amino acid residue is carried, and thus not only is the good 
biology activity of interest protein products ensured, but also multicopy cutting cost is saved, the purification is simple and the 
mass production is facilitated.