The composite steel structure combines the advantages of steel structures and concrete structures. In order to study the energy-saving behavior of the composite steel structure, a thermal testing on a typical composite steel structure residential in cold region is performed. The energy consumption performances of all components of the residential are evaluated; the heat transfer coefficient K for envelope structure is obtained using the testing data and then the K value is compared with the current specification. The results show that energy-saving standard of the testing residential could not meet the requirements of code. Finally the existing problems and solutions for the composite steel residential buildings are produced.