Abstract: The protective green spaces on both sides of urban railway corridors have been abandoned for a long time, while railway lines in operation have reserved a large quantity of protective green spaces for cities. This research aims to, under the premise of satisfying the requirements for sound insulation and protection functions, explore the potential and opportunities of railway corridor green spaces to provide cultural ecosystem services (CES) for urban spaces along railway corridors. Taking green spaces on both sides of the Beijing-Guangzhou Railway (high-speed) and Beijing-Guangzhou Railway (general-speed) in the central urban area of Beijing as research objects, and urban spaces extending 1 km on both sides of the aforesaid railway lines as research scope, this research establishes a research framework for CES supply by railway green corridor based on existing Researches, including both CES supply potential (CSP) and CES supply opportunity (CSO). The research believes that: 1) existing landscape elements can be transformed into the five categories of plants, water bodies, recreational activities, site and traffic, and management and maintenance, meanwhile the elements to be supplemented mainly focus on the improvement of facilities and final-period management and maintenance, for which the approach of “identification-transformation and supplement-supply” is put forward; 2) within the research scope, CSO along railway corridor is relatively high in the area extending from the West 3rd Ring Road to the West 5th Ring Road, medium in the area located south of the Beijing Garden Expo, and relatively low in the area extending from the eastern boundary to the West 3rd Ring Road and the Beijing Garden Expo area. Based on the above results, the research puts forward specific suggestions for CES supply by railway corridor green spaces. The research on CSP and CSO of railway corridor green spaces is a quantitative spatial research on CES functions at the mesoscale, which will provide basic materials and theoretical reference for fine governance of traffic spaces along railway lines.