既有商品住宅节能改造具有一定程度的外部性，阻碍了节能改造的深入开展。通过分析节能改造外部性的产生原因和外部性表现，建立外部性测算方法，为外部性内部化，构建节能改造外部性偿还机制提供必要依据。采用经济学理论与方法对既有商品住宅节能改造外部性的产生和表现等进行了分析，在识别外部性供体与受体的基础上，提出了节能改造外部性的测算方法。通过案例分析论证了外部性测算方法的适用性。结果表明，应减轻或消除外部性对节能改造的影响，采取必要手段将节能改造外部性内部化，构建统一的节能改造外部性测算方法，建立节能改造外部性偿还与节能量交易机制。

Externality exists in the field of existing commercial residential buildings energy-saving retrofit which hinders the implementation of energy-saving in-depth. To build the externality calculation method in order to provide the necessary basis for the internalization of externality and the establishment of energy-saving externality repayment mechanism. To describe the causes and manifestations of energy-saving externality by economic theory and method. To propose the calculation method on the basis of identifying the externality donors and acceptors. To demonstrate the applicability of the calculation method externality through case analysis. The conclusions show that the externality should be reduced or eliminated; the necessary means should be adopted to internalize the externality of energy-saving retrofit by building a unified external energy saving calculation method, establishing energy-saving retrofit externality repayment and energy savings trading mechanism.