Abstract: CTCS3-300H ATP on-board equipment safety computer exchanges information with peripheral sub-system through HDLC communication interface. It has the characteristics of mature and stable. The RS-422 serial port was used for the CFSK board communication interface of CTCS2-200C ATP on-board equipment. In order to make CFSK board used by CTCS2-200C ATP implement the track circuit reading function in TCS3-300H ATP on-board equipment, it was needed to design and develop the interface adaptation. The communication board of track circuit subsystem was designed to implement the conversion function between RS-422 serial port and HDLC communication interface, make CFSK board adapt to CTCS3-300H ATP on-board equipment safety computer.