A signal equipment improvement project for the existing facility ATS to ATP is under construction in Kyung-Bu and Ho-Nam commercial line including 400 rolling stocks. But there was a concern for the interface between KTX OBCS and ATP from the beginning of the project. At present, this is the front burner event. This paper introduces interface checking and predicted failure point between KTX OBCS and ATP improvement system. Through this measure the optimal installation of the ATP will be possible. The study was made under maintenance efficiency including reliability because the KTX signal equipment must qualify the above condition.