The invention discloses a data encryption method and system conducting terminal data backup through a server. The method includes the steps that firstly, a backup terminal initiates a backup request, and the server sends a public key of the server to the backup terminal; secondly, the backup terminal generates a work key, and the work key is used for encrypting backup data to form a backup ciphertext; thirdly, the public key of the server is used for encrypting the work key to form a ciphertext of the work key, and the backup ciphertext and the ciphertext of the work key are sent to the server to be stored; fourthly, a recovery terminal initiates a recovery request and sends a public key of the recovery terminal to the server, the server decrypts the ciphertext of the work key, and the public key of the recovery terminal is used for encrypting the work key; fifthly, the backup ciphertext and the ciphertext of the work key are sent to the recovery terminal; sixthly, the recovery terminal decrypts the ciphertext of the work key through a private key of the recovery terminal so as to obtain the work key, the work key is used for decrypting the backup ciphertext, and a plaintext of the backup data is obtained.