<p>Dangerous rock masses in mountainous areas seriously threaten the construction and operation of engineering with potential disaster hazards, especially the unpredictability and sudden occurrence of rockfall, which poses a huge challenge. This paper presents a systematic risk assessment and disposal of high and steep giant dangerous rock masses, which can pose a serious threat to railway operation. Using comprehensive methods such as on-site investigation, limit equilibrium method, and simulation analysis of rockfall trajectory, the possibility and potential harm of collapse and rockfall of giant dangerous rock masses are analyzed and corresponding remediation measures are proposed. Because of the huge size of the dangerous rock mass, the cracks behind the upper part of it are all penetrated; the overturning moment is 500,033.29kN·m, and the safety factor is only 0.744 under the most unfavorable working condition in terms of seismic action. Once the dangerous rock body collapses, most of the rockfalls occur near the tunnel portal and the railway bridge with large velocity and high kinetic energy and jump height. A safe and durable anchoring method of a prestressed anchor cable with double anchoring sections is proposed for in-situ reinforcement of giant dangerous rock masses to prevent the occurrence of collapse and rockfall disasters. The development of this method suggests new ideas and new methods for the reinforcement of similar dangerous rock masses.</p>