The invention provides a Sybil attack defense method comprising the steps of an initialization step including using a secret key generation center to run a preset setting algorithm to generate a main key MSK={S} and release a public parameter pp according to an known safety parameter lambda and an overall attribute set U; a registration step including submitting a registration request to the secret key generation center via a user, generating a user private key SKS through running a preset secret key generation algorithm by the secret key generation center, and distributing the user private key SKS to the user via a secret channel; a signature step including performing signature through running a preset signature algorithm by the user; and a verification step including verifying a signature through running a preset verification algorithm by the user after signature. The invention also provides a Sybil attack defense system. According to the technical scheme of the method and the system provided by the invention, Sybil attacks can be effectively defended, and data security is improved.