Head-Up Display (HUD) is a critical system that impact aircraft flight safety. If it is invalidated, it will lead to the catastrophic accident of controlled flight into terrain. The traditional safety assessment based on independent component failure cannot be adaptive to the feature of the integrated modular avionics system, which is highly coupling and is hardware resource sharing. And thus it is difficult to achieve a comprehensive and effective safety analysis. By using Safety Case theory, we built up a safety assessment model of HUD and established traceability between safety goals and safety solutions, to achieve assessing the safety of HUD. The results showed that: the safety analysis model of civil aircraft HUD system based on Safety Case can elaborate that system safety objectives are met by safety evidences.