由于城市社会、经济、人口、空间、布局等的发展变化，既有地铁线路可能出现不再适应城市区域新发展的情况，局部线路面临调整、改造的问题。分析温哥华空中列车世博线和千禧线、东京地铁副都心线和东急东横线、北京地铁 13 号线和广州地铁 3 号线的改造原因、方案及效果，并在此基础上总结概括既有地铁线路改造的一般原因、典型方法。客流需求改变和城市结构变化是线路改造的主要原因，常以减少换乘次数、缓解换乘站 客流压力、优化客流分布、扩大线网覆盖面、缩短行车间隔等为目标，采用直通化、拆分重组、延展扩建等方式 进行。
Due to changes in urban society structures, economy, population, space, and layout, some existing metro lines may no longer be perfectly suitable to the new needs of some urban districts. Therefore, some lines are faced with the need for adjustment and reform. This study analyzes the reasons, schemes, and effects of the renovation of the Expo and Millennium Lines of the Vancouver Skytrain, Fukutoshin and Tokyu Toyoko Lines of the Tokyo Metro, Line 13 of the Beijing Metro, and Line 3 of the Guangzhou Metro, and summarizes the general reasons and typical methods of existing metro lines renovation based on these cases. The main reasons for metro line renovations are changes in passenger demand and urban structure. Some common methods used in these instances are, among others, connecting two independent lines, line splitting and reorganization, and line extensions, which are all aimed at reducing the number of transfers, reducing number of transfer passengers at transfer stations, optimizing the distribution of the passenger flow, expanding the coverage of the metro network, and shortening the departure interval.