The invention relates to a multifunctional nano-
drug carrier, a preparation method thereof and a 
drug-loading composition, and belongs to the technical field of biomedical 
drug carriers and sustained-release drug carriers. The nano-
drug carrier is formed by self-assembling a poly-seleno-
amino acid amphiphilic block 
copolymer with a structure shown in the following formula, wherein n is more than or equal to 22 and less than or equal to 454, x is more than or equal to 2 and less than or equal to 50, y is more than or equal to 2 and less than or equal to 50, and n, x and y are integers. The nano-
drug carrier provided by the invention can load drug molecules to prepare a sustained-release and controlled-release 
drug delivery system, and can be used for 
drug delivery in various 
modes, and theloaded drug can be released from the 
delivery system in a sustained-release and controlled-release mode according to needs, so that the 
drug delivery frequency is reduced, the 
treatment effect is improved, and the toxic and side effects of the drug are reduced. Compared with the prior art, the nano-
drug carrier provided by the invention has the advantages of a common 
amino acid nano-drug carrier,has a plurality of biological functions of 
selenium, and is a novel multifunctional nano-drug carrier.