Aggregate signature can aggregate n signatures on n messages from n signers into a single signature that convinces any verifier that n signers sign the n messages,respectively. In this paper,by combining certificateless public key cryptography and aggregate signatures,we propose an efficient certificateless aggregate signature scheme and prove its security. The new scheme is proved secure against the two representative types adversaries in certificateless aggregate signature under the assumption that computational Diffie-Hellman problem is hard. Furthermore,from the comparison of the computation cost of the new scheme with some existing certificateless aggregate signature schemes in group sum computation,scalar multiplication computation,Hash computation and abilinear pairings computation,it concludes that the new scheme reduces the computation cost in scalar multiplication computation in half and maintains the same in the other computation costs. Aggregate signature can aggregate n signatures on n messages from n signers into a single signature that convinces any verifier that n signers sign the n messages, respectively. In this paper, by combining certificateless public key cryptography and aggregate signatures, we propose an efficient certificateless aggregate signature scheme and prove its security. The new scheme is proved secure against the two representative types adversaries in certificateless aggregate signature under the assumption that computational Diffie-Hellman problem is hard. Furthermore, from the comparison of the comparison cost the new scheme with some existing certificateless aggregate signature schemes in group sum computation, scalar multiplication computation, it concludes that the new scheme reduces the computation cost in scalar multiplication computation in half and maintains the same in the other computation costs.