The invention discloses a sterilization / endotoxin neutralization polypeptide modified by polyethylene glycol, which consists of a formula as follows: X-Y-BNEP-OH or H-BNEP(i-Y-X)-OH, wherein, X is polyethylene glycol or single-methoxy polyethylene glycol, Y is a linking group, i is 1 or 3 or 13 or 14, representing the position number of lysine with a modified on side-chain amino group in an amino acid sequence; and BNEP is the sterilization / endotoxin neutralization polypeptide which has an amino acid sequence shown by SEQ ID No.1; the modification polypeptide, while maintaining the endotoxin neutralization activity of BNEP, prolongs the half-life in vivo of BNEP, and shows potential for being developed into new endotoxin neutralization medicaments, thus being capable of providing new curative medicaments for treating patients of severe diseases such as pyaemia, septic shock and the like. The invention also discloses a preparation method of the modification polypeptide, which has high product yield and high purity, thus being capable of realizing fixed-point modification of polyethylene glycol of synthetic polypeptide.