Aiming at the security problems existed in most identity-based threshold ring signature (ITRS) schemes, including poor security and inefficient in verifying, a new ITRS scheme is proposed. We significantly enhance the security of signature key by using bilinear pairings and secret sharing techniques. Our analysis indicates that the proposed scheme achieves unconditional anonymity and unforgeability. A security problem (ring member-changing attack) also can be solved. Compared to the congener schemes, ours is much more efficient in signing process.