This study describes the results of Preliminary Hazard Analysis (PHA) performed for Train Control System (TCS) of Honam KTX Line. PHA is performed to identify hazards at system level based on the risk-based approach followed by IEC 61508 and other relevant international standards. The hazards are firstly classified by the operational functions of railway system proposed by AEIF (The European Association for Railway Interoperability). Then, the hazards are identified in more detail according to the function of TCS in the process of the railway operation. In doing this, the relevant equipment among TCS are identified. The result shows that PHA can be used to demonstrate which hazard could be expected and which consequences could occur in the process of railway operation as the result of their functional failure(s). This way of description is a starting point for an operation or technical realization demanding TCS. In addition, the result can be used for allocating Safety Integrity Level (Sn") for each subsystem composing TCS and for generating any safety requirements that might not be taken into account in the system requirements.