Mechanical properties of CA mortar with different air content were studied, and the size of the air bubbles was also analyzed. Results showed that the ductibility of CA mortar could be largely prolonged by the air bubbles. As the air content of CA mortar increased from 4.2% to 9.1%, the strain of the maximum stress increased from 1% to 2%. The compressive strength and elastic modulus of CA mortar decreased as the air content increased. And when the air content of CA mortar was higher than 15%, the compressive strength of it decreased rapidly. The SEM analysis showed the air bubbles of diameter larger than 0.5mm was the primary reason of decrease of the compressive strength.