In order to attain the higher efficiency, SOFC(solid oxide fuel cell) is used in a cogeneration system. This paper first introduces the cogeneration system for buildings which makes good use of power and heat energy. Power energy used for domestic loads and the surplus can be provided for utility grid. Exhaust heat from the reactor can be used for water and space heating, and also can be used for absorption heat pump to supply cooling. Then the demonstration projects are given. Through the analysis of the cases, discusses the exiting challenges in the SOFC for building applications.