In this work, the composites based on long glass fiber reinforced polypropylene/intumescent flame retardant (LGFPP/IFR) were prepared by melt blending. This article presented an experimental research on the influence of combined environment elements in natural condition on the properties of LGFPP/IFR composites with 0-12 months ageing. The flammability and thermal properties of the composites were investigated by limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), thermal gravimetric analysis (TGA), mechanical properties test and energy dispersive X-ray analysis (EDAX). The LOI values increased from 27.5 to 28.3 in 0-6 months ageing, and then decreased back, however, the TGA curves shift to the lower temperature. The thermal degradation kinetics were analyzed and the apparent active energy (E) of aged and unaged samples were calculated by Flynn-Wall-Ozawa method. The results indicated that much lower E values were obtained after 3-12 months ageing. EDAX data proved that the IFR particles gathered on the surface of samples in natural exposing, by which had some effect on the thermal stability and flame retardancy of the composites. The mechanical properties showed a global decrease in the whole ageing period by matrix degradation and interface debonding under the influence of combined environment elements. POLYM. ENG. SCI., 58:2098-2105, 2018. (c) 2018 Society of Plastics Engineers