The aging properties of advanced composite T300/5405 which soaked in 15# hydraulic oil, 4010 lubricating oil, RP-3 kerosene and AHC-1 cleaner were studied. The absorption and mechanical properties of the composites were measured, and the scanning electron microscopy(SEM), dynamic mechanical analysis(DMA) and the infrared analysis(IR) were used to investigate the properties’ changes of the composite. The aging mechanism of composite T300/5405 was also discussed. The experimental results show that the absorption of the composite in AHC-1 was the biggest, and the other three mediums had little effect on the composites. The mechanical properties declined in the aging. The composites have undergone chemical change in the test; T g rose or declined after the aging, and the AHC-1 cleaner and 4010 lubricating oil had the greatest influence on the T g. The aging properties of the advanced composite T300 / 5405 which soaked in 15 # hydraulic oil, 4010 lubricating oil, RP-3 kerosene and AHC-1 cleaner were studied. The absorption and mechanical properties of the composites were measured, and the scanning electron microscopy SEM; mechanical mechanical analysis (DMA) and the infrared analysis (IR) were used to investigate the properties’ changes of the composite. The aging mechanism of composite T300 / 5405 was also discussed. The experimental results show that the absorption of the composite The composites have undergone chemical change in the test; T g rose or declined after the aging, and the AHC -1 cleaner and 4010 lubricating oil had the greatest influence on the T g.