In order to investigate the effect of low air pressure on the air entrainment of cement-based materials, simulation study of negative pressure was conducted. The foaming performance and bubble stability of air-entraining agent (AEA) solution, pore structure of air-entrained cement paste, and air-void structure of air-entrained cement mortar were tested in different air pressures. The cement paste and cement mortar specimens were stirred and formed in designed air pressures until hardening. Results show that the foams formed by two new types of AEAs (FC-1 and FC-2) were more stable than those formed by triterpenoid saponin type AEA (SJ-2) in corresponding aqueous solutions in negative pressure. However, this finding could not be extended broader to cover cement-based materials. The total porosity and the volume of pores with radii of 100-1 000 nm in hardened cement paste were found higher in negative pressure, while there was little adverse effect of low air pressure on either air content or air-void structure of hardened cement mortar when a suitable AEA was applied. SJ-2, FC-1, and FC-2 AEAs could satisfy the requirements of air entrainment for frost resistant concrete in high-altitude regions with low air pressure, among which FC-1 and FC-2 presented comparative advantages in air-void structure optimization and air content control.