In order to eliminate the inherent key escrow problem in identity-based public key cryptosystem,a new identity-based blind signature scheme without trusted Private Key Generator(PKG) was proposed.Under the random oracle model,the scheme was proved to be existentially unforgeable against adaptive chosen message and identity attacks from common attackers or semi-honest PKG,and the security was reduced to computational Diffie-Hellman assumption.For the forgery attacks from the malicious PKG,the legitimate signer can prove to the arbitration institution that the signature is forged by trace algorithm.