Abstract: The quality of insulation directly affects the energy consumption of buildings. In order to save energy and improve the living environment of employees, a company carried out energy-saving modification of a large number of old residential buildings. Polystyrene insulation system with thin plaster layer was used. It has advantages of good insulation effect and easy construction, but has problem of surface cracking. In order to solve the surface cracking problem and enhance the energy saving and insulation effect, a special research was carried out before the implementation of the project. The reasons for cracks in polystyrene insulation system with thin plaster layer were analyzed, comprehensive measures were taken to avoid cracking, and desired results were achieved

Key words: thin plaster layer, polystyrene, crack, quality control