A data assured deletion approach adapted for cloud storage is proposed to protect data confidentiality of cloud storage system.We utilize a key derivation tree to organize and manage keys which are pushed to DHT network after partitioned by secret sharing scheme.The dynamic property of DHT network makes keys be deleted periodically causing ciphertext can not be decrypted or accessed when authorized time expires.And data assured deletion is implemented.The experiment results show that this method can delete keys effectively and the performance is low.It suffices for the requirements of assured deletion of expired data or expired data in the cloud storage system.