Dynamic compression test of cement asphalt（CA） mortar specimens immersed in water for 0, 7, 14, 30, 60d, was carried out using an electronic universal test machine with the strain rates ranging from 1×10-5s-1 to 1×10-2s-1. The stress strain full curves, the compressive strength, the elastic modulus and the peak strain of CA mortar at different strain rates and water immersion durations were analyzed and the effects of strain rates and water immersion duration on these dynamic behaviors were studied. Results show that the mechanical property of CA mortar is affected significantly by strain rates and water immersion duration. The compressive strength and elastic modulus increase with increasing strain rate. In the same strain rate, the compressive strength and elastic modulus decrease first and then increase with increasing of water immersion duration. The largest reduction of average compressive strength of CA mortar is 4631%, and the largest reduction of elastic modulus of CA mortar is 4491%. The peak strain of CA mortar shows a trend of increase with the strain rates and water immersion, and the influence of water immersion time on the peak strain is larger than that of the strain rate.