A method and a system for continuously transmitting railroad information between an on-board controller and a ground controller. A redundancy code which is updated according to a preset procedure at every transmission is added to the information to be transmitted, and the resultant is transmitted. On the receiving side, the redundancy code received together with the transmitting information is collated with a redundancy code which is prepared on the receiving side and updated according to a preset procedure. Therefore, the fault of the transmission route is detected easily, and the safety of train by means of the automatic train control is improved.