The security of XUE-CAO proxy blind signature scheme was analyzed, and two forgery attacks,which make the original signer or any other third party can forge a valid proxy blind signature,were pointed out. Furthermore，to improve XUE-CAO scheme，an improved proxy blind signature scheme is proposed. While reserving the advantages of the original scheme, this scheme is capable of resisting any forgery attack,which can be used to build more secure system.
