Partially blind signature is designed to adress the contradiction between anonymity and controllability, and it can protect the privacy of users and trace user identity when it is necessary. The problem is that the public information can be tampered by malicious parties, which exists in partially blind signature schemes based on identity. Security analysis of the Liu scheme shows that the user can modify public information illegally. On this basis, we propose an improved IDbased  partially blind signature. Based on the discrete logarithm problem, this scheme can satisfy the requirement of partial blindness while being capable of resisting against existential unforgeability attack of the adaptive chosen message under the random oracle model. The new scheme does not use the bilinear pairing operation with higher computational cost, and avoids public information tampering. Compared with existing schemes, it improves security and efficiency significantly.