Computer is the vital element for safety-critical control system. This paper presents a component-based fail-safe computer in railway signal interlocking system (safety interlock computer - SIC). We discuss the methodology and the safety tactics of SIC in detail, moreover, the architecture and safety computation principle are deeply analyzed. The hardware safety integrity level of SIC has been verified according to standard IEC 61508, and the result shows that SIL4 is achieved, and SIC fulfils the rigorous safety requirements of signal interlocking.