Abstract: To generalize the concept of (t,l)threshold proxy signature scheme, this paper proposed a (t, k, l)threshold proxy signature scheme, in which any k or more proxy signers in a designated proxy group of l members can cooperatively issue a proxy signature and this scheme can also tolerate at most t-1 corrupted signers. The security model of existential unforgeability for the threshold proxy signature scheme was presented, then a (t +1, 2t +1, l)threshold proxy signature scheme based on the hardness of CDH problem was proposed, and the existential unforgeability was proved under this security model. At the same time, this scheme has the properties of distinguishability and proxy protected.