The foaming performances of two air entraining agents(AEA), including AES and 303R, in Beijing, Chuxiong, and Shigatse were respectively investigated to study the effect of air pressure on air entrainment of cement based materials. The foaming performances were assessed by size and development of bubbles in water solution, pore size distribution in hardened cement paste, and apparent densities of hardened cement paste and mortar. The results show that as the atmospheric pressure decreases, initial air bubbles in both two AEA solutions become larger. Larger initial bubbles are less stable as they engulfed surrounding small bubbles more quickly. Bubbles foamed by 303R are obviously smaller than those foamed by AES, indicating that 303R has superiorities in bubble stability and adaptability to plateau environments. As the atmospheric pressure decreases, the apparent density of hardened cement paste decreases, and the percentage of large pores increases. The ranking about cumulative volume of pores with radius between 1001000nm is Shigaste>Chuxiong>Beijing. Additionally, the apparent density of cement mortar slightly increases, indicating a little air content reduction, as the atmospheric decreases. However, the air content of mortar reduction is no more than 21%(equivalent to 12% for concrete).