Spherical closed voids in cement asphalt(CA) mortar were measured by image analysis(IA) method. Connected pores in CA mortar were measured by mercury intrusion porosimetry(MIP), constant temperature and humidity drying(CTHD) method and nuclear magnetic resonance(NMR) method. The results show that the average diameter of closed voids is about 150μm. The porosity（by volume） of closed voids is depending on the air content and the amount of aluminum powder in fresh CA mortar and its maximum value is more than 20%. The radius of connected pores is 10100nm. The larger the water cement ratio in fresh CA mortar, the higher the porosity of connected pores. It is found that the total porosity of connected pores in CA mortar obtained by NMR, MIP and CHDT methods is similar. NMR and MIP methods can get continuous pore size distribution, while CTHD method cant. Comparing MIP and NMR methods, some damage of the microstructure in CA mortar is able to occur during drying and measuring process in the former, but is not due to the specimens saturated with water in the latter. NMR method is the best method to accurately measure and characterize the original connected pore structure of CA mortar.