Abstract:Thi s ar ticle ex plains the properties of the UEA ex pansive agent fo r cement and analyses the mechanism of self-w aterproof o f the cement mix ed wi th UEA expansiv e agent. acco rding to the physical-mechanical pro perties test resul ts of the cement mix ed wi th UEA ex pansiv e ag ent and i ts engineering application at the selected point , the autho rs draw a conclusion - mixing the UEA ex pansiv e agent into cement is an ef fectiv e measure to make the cement inner lining of tunnel having self-w aterproo f pro perty.