An entity bi-directional identification method and system based on a trustable third party thereof are provided. The system comprises a first entity, which is for sending a first message to a second entity, sending a third message to a third entity after receiving a second message sent by the second entity, verifying the fourth message after receiving a fourth message sent by the third entity, sending a fifth message to the second entity after the verification is finished; the second entity, which is for receiving the first message sent by the first entity, sending the second message to the first entity, verifying the fifth message after receiving the fifth message sent by the first entity; the third entity, which is for receiving the third message sent by the first entity, checking if the first entity and the second entity are legal, implementing the pretreatment according to the checking result, sending the first entity the fourth message after the treatment is finished.