Relationship between the fire resistance of thin plastering external thermal insulation system (TPETIS) and the combustion property of foam plastic core materials was explored based on standard combustion test and real scale fire test. The results show that fire growth rate index, peak heat release rate and oxygen index are key factors that influence the fire resistance of TPETIS in the condition of same system configuration.When exposed to window spill plume, TPETIS with core materials having a classification of combustion property of B or C has relatively low risks of surface fire propagation, internal fire spread and smoke layer heat radiation in the upper room. TPETIS with class D core materials has some risk of internal fire spread and smoke layer heat radiation.