The Fifth Generation of Mobile Communications for Railways (5G-R) brings significant opportunities for the rail industry. However, alongside the potential and benefits of the railway 5G network are complex security challenges. Ensuring the security and reliability of railway 5G networks is therefore essential. This paper presents a detailed examination of security assessment techniques for railway 5G networks, focusing on addressing the unique security challenges in this field. In this paper, various security requirements in railway 5G networks are analyzed, and specific processes and methods for conducting comprehensive security risk assessments are presented. This study provides a framework for securing railway 5G network development and ensuring its long-term sustainability.