It can be found from the KW 2449 between Figs. 6 and 7 that water–cement ratio has a crucial influence on pore structure. With the increase of water–cement ratio, the surface tensile force of cement paste decreases so that pores are damaged seriously. Comparison of Figs. 6 and 7, when the water–cement ratio increased from 0.8 to 0.90, the pores are damaged obviously and the uniformity of pore size also decreased significantly. The pore structure is a key factor to affect the properties of cement-based foam material, including pore sizes, pore shape and pore connection, etc. The analysis shows that pore structure is influenced by the setting time of the cement paste and the stability of foam in cement paste. The variation in water–cement ratio has changed the consistence of cement paste, whereby affecting the cement paste setting time and foam curing speed. HPMC admixture could improve the flexibility and mechanical strength of the cement paste liquid film so that it is favorable for improving pore structure too.