Moisture content, water saturation and frost resistance of cement asphalt mortar(CAM) in China railway traffic systemⅡ(CRTS Ⅱ) ballastless slab track under humidityinsulation curing for 28 d have been studied. The results showed that the water saturation of the CAM under humidityinsulation curing for 28 d was about 86.1%（by mass）. The CAM might be damaged during freezethaw process while the specimens were surfaceimmersed in the water, the surfacescaling amount of which keeps arising with increasing of the freezethaw cycles. However, CAM still showed excellent frost resistance with far lower surfacescaling amount than the requirement after 188 freezethaw cycles and will never be damaged for the specimens being freezethawed under humidityinsulation condition. After CAM was dried, the speed of water readsorption was very slow and the water saturation was only 50.5% even the dried CAM was immersed in water for 19 d due to hydrophobic behavior of the asphalt in the CAM. In actual projects, hardened CAM was often dried to lower watersaturation, thus it is impossible to be damaged due to freezethaw of the water in the CAM.