The fast development of big data computing contributes to the fact that large-scale graph processing has become a basic computing model in both academic and industrial communities, and it has been applied in many actual big data computing works, such as social network analysis, Web search, and product promotion. These computing works include large-scale graphs of billions of vertices and trillions of edges. Such scale has brought many challenges to large-scale graph processing. This paper mainly introduces the essential features and challenges of large-scale graph processing and how we can handle billions of edges on a multi-core machine, for which we represent out-of-core processing system and semi-external memory processing systems. This paper also summarizes the key technologies in graph processing systems and forecasts the future development of large-scale graph processing systems.