北京地铁4号线和伦敦地铁都是通过公私合营（PPP）的方式与融资能力强、具有一定经验的社会资本合作，北京地铁4号线自2009年开通以来一直运行良好，伦敦地铁PPP项目在运营不到7年就宣布破产。运用比较分析方法从融资结构、运营管理和合同履行3个方面对北京地铁4号线和伦敦地铁进行分析，发现伦敦地铁失败的原因主要是其融资结构不合理，竞争机制不完善，契约精神缺失，并针对这些问题为以后PPP项目的实践提出3点建议： 1）在伙伴选择方面，引入竞争机制，项目公司市场化运营； 2）优化融资结构，合理分担风险； 3）强化契约精神，加强政府监管。

Beijing fourth line and London Underground both corporated with social capital by way of franchising, who has strong financing capacity and extensive experiences. Beijing fourth line has been running well since opening in 2009, while London PPP project was declared bankruptcy in less than seven years of operations. This article analyzes Beijing subway line 4 and London Underground mainly from the financing structure, operation mechanism and the performance of the contract three aspects, finding that unreasonable financing structure, imperfect competition mechanism and lack of spirit of contract are the main cause of the failure of the London Underground. To solve these problems, the author puts forward three suggestions: (1) in the partner selection, to bring in competition mechanism, and the operation of project companies should be market-oriented; (2) to optimize the financing structure, rationalise risk-sharing; (3) to strengthen the spirit of the contract and government regulation.