The invention discloses an encryption method and an encryption device of a mobile terminal memory card as well as a mobile terminal, and relates to a mobile communication technology. The method comprises the steps of detecting a screen locking event and a screen unlocking event in real time by the mobile terminal; when the screen locking event is detected, acquiring and storing key information used for reading file content of the memory card in the memory card by the mobile terminal, and carrying out encryption treatment on the memory card by utilizing the key information; when the screen unlocking event is detected, carrying out decryption treatment on the memory card by the mobile terminal by utilizing the stored key information. The encryption method and the encryption device of the mobile terminal memory card are capable of automatically triggering the encryption and the decryption functions of the memory card, and the user experience is not influenced.