The problem of key management in ad hoc networks was analyzed. Based on the elliptic curve Paillier scheme and Shamir secret sharing scheme, a new key management scheme that adapts to ad hoc networks was proposed. In this scheme, the new node provided elliptic curve Paillier scheme to the authentication nodes in the system, and kept the corresponding trapdoor secret. Making use of the homeostasis of elliptic curve Paillier scheme, the nodes that participate in the key distribution encrypted the corresponding shadows and added them one by one. At last, the sum was sent to the new node and was decrypted. In order to prevent the attacker who came from the system, the shuffling factors were added to the encryption. The new scheme has better security, and the difficulties to break it are not less than to break RSA.