Crack resistance is one of the key technologies to be solved by the external thermal insulation technology system of the external wall, because once the thermal insulation layer and the protective layer crack, the thermal insulation performance of the wall will be greatly changed, which can not meet the energy-saving requirements of the design, and even endanger the safety of the wall. In a very long period of time, there are quite a number of projects with cracks in the thermal insulation wall that have not been effectively solved, The research on crack resistance technology of external thermal insulation wall is still in its infancy. What is harmful crack and what is harmless crack in thermal insulation wall needs to be further determined through tests.