According to the characteristics of intercity train, the necessity of intercity train bringing in ATO system from three aspects about automatic train driving, automatic closing and opening passenger doors and linkage with shielding doors in station, and automatic reverse was expounded. The additional signal interface between vehicle and ATO system after introducing ATO system into intercity train was analyzed and summarized, and the new equipment of onboard signal system in order to meet the ATO function was described. The interface design was validated in practical projects test.