Forward security and blind signature become hot spots in the researches of cryptography. Forward-secure digital signature can effectively reduce the loss that aroused for the reason of secret keys exposure. Blind signature plays an important role in protecting the senders' privacy. This paper proposes a new conception named correlative-factor, and by which a forward-secure blind signature scheme based on ElGamal is designed. Forward security is applied to a blind signature scheme in this paper. Through the detailed analysis of security, the proposed scheme not only has the features of forward-secure, weak blindness and resisting forging attack, but also has certain theory and practical values.