The effect of non ionic cellulose ethers（NCE） with different molecular structure on pore structure of cement pastes was investigated by apparent density test, visual observation, optical microscope and SEM. The results indicate that the addition of NCE results in higher porosity in cement pastes. The porosity in cement pastes modified by hydroxyethyl cellulose ethers（HEC） is lower than that in cement pastes modified by hydroxypropyl methyl cellulose ethers（HPMC） and methyl cellulose ethers（MC） when their viscosity is close to each other. If HPMC with close substituent group content(by mass) is added, the lower the viscosity/relative molecular mass of HPMC, the lower the porosity of the cement pastes. The addition of NCE reduces the surface tension of liquid in cement pastes and leads to form bubble more easily. The ability of cement pastes to stabilize bubbles is enhanced by the addition of NCE because NCE molecules are adsorbed on the gas liquid interface of bubbles orientationally and the viscosity of cement paste is increased.