The invention relates to a polypeptide with tumor-targeting performance and a preparation method. The structure of the aminophenol sequence of the polypeptide is CASPSGALRSC or CFPVPGHDLVC or CFSVPGHDIVC or CTPMSLSLSEC or CYTYPLGWHIC. The pC89 phage 
peptide library expressing 
protein polypeptides with different sequences of 108 and 
human breast cancer cell lines MDA-MB-231 are repetitively cocultured for a few times; 
filtration can penetrate 
cell membrane to enter into the phages expressing specific polypeptide in cytolymph and  /  or karyon, and phages are amplified 
in vitro in order to carry out 
DNA sequencing and deduce an exogenous 
amino acid sequence inserted in the phages; the filtered specific polypeptide phages, other 
human tumor cells and normal cells are cocultured 
in vitro, and the tumor 
cell specificity of the polypeptide phages is tested; according to the testing results of polypeptide sequence and cell specificity, the polypeptide with 
tumor targeting is artifically synthesized. The invention as a specificity carrier of the mammary 
cancer-targeting 
genetic therapy has potential clinic application value. The invention also provides a strong 
technical support for the 
filtration of affinity specificity polypeptide of other types of malignant tumor cell strains. Moreover, the polypeptide only contains nine to eleven 
amino acid residues, so the polypeptide can be easily synthesized, the change of spacial position is relatively less, the 
quality control of the polypeptide is easy, and use is convenient.