Nano SiO2 blended cement pastes for grouting soil nailing were produced， using hydrophilic nano SiO2 powders and P·Ⅰ42.5 cement as raw materials. Bleeding height， slump extension and strength of cement pastes containing different contents of nano SiO2 powders were measured. Microstructures and composition of nano SiO2 blended cement pastes at different ages were investigated by X ray diffractometry（XRD） and thermal gravity differential thermal analysis（TG DTA）. The results show that bleeding height and slump extension of cement pastes decreased with increasing nano SiO2 content. By blending nano SiO2 powders into cement pastes， the flexural strength and compressive strength of hardened cement pastes are enhanced， especially at later age. The optimum nano SiO2 content is 1.0%2.0%. Nano SiO2 blended cement pastes contain less Ca（OH）2 and more C S H gel than pure cement paste.