The healthy and stable development of energy efficiencies in existing buildings cannot be separated from effective policy operation, and evaluating policy effectiveness contributes to scientifically-sound government decision-making. This paper creates an evaluation index system and a grey comprehensive evaluation model for policy effectiveness for energy efficiency in existing buildings using three dimensions: 1) the effect of the policy itself; 2) the administrative effect of the policy; and 3) policy implementation effects. It chooses the government’s subsidy policy and preferential tax policy at market cultivation stage for its empirical comparative evaluation. The evaluation indicates that the former is more effective. Finally, it puts forward policy development suggestions from the perspective of: 1) clarifying incentive object; 2) broadening incentive scope; 3) increasing incentive intensity; and 4) innovating incentive mode.