Abstract: This paper proposes two kinds of technology to defend portable executable file viruses.The first technology analyses the format of portable executable file and the ways that virus infects the portable executable file,and thus defend viruses through improving the self-structure of portable executable file;The other technology is a kind of computer virus immune method which is based on self-integrality examination of portable executable file. It adopts unilateralist hashing function MD5 algorithm to acquire abstract.We judge whether it has viruses by comparing the two abstract values,and start resuming procedure to resume file if it has viruses.Compared with traditional character code matching method,these technology can prevent unknown viruses without virus library.