The purpose of this study is to clarify the strategy of policies that aim to reduce greenhouse gas of existing houses in Germany. Major methods of this study include literature survey analysis and interview of relevant organizations of Germany. In this study, we analyzed the strategy of policies in three aspects: regulatory strategy, financial strategy and informative strategy. Results of the study are as follows. Low energy performance on specific component of existing housings to meet the current standards is becoming mandatory. In addition, housing renovation is stimulated to high energy performance work by graded financial support. Germany government is built up the information system of the Internet, publications, expert advice, the hotline to provide the citizens with the government strategy. These $CO_2$ reduction strategies is the relationship with each other organically and have encouraged the participation of the citizens to greenhouse gas reduction activity. Finally, directions for the energy efficiency improvement policies of existing housing stock in Korea were proposed.