The synthesized nano-SiO2 was attached to the surface of polyvinyl alcohol (PVA) fiber and polyethylene (PE) fiber by chemical deposition method, and the distribution of SiO2 on the modified fiber surface was observed by scanning electron microscope (SEM). The strength and toughness of engineering geopolymer composites (EGC) were compared by compressive tests, flexural tests and uniaxial tensile tests before and after the surface modification of fibers. And the reason for the change of macro-mechanical properties was verified by single fiber pull-out tests from the microscopic mechanical point of view. The results show that the compressive and flexural strength of PVA fiber EGC specimen after hydrophobic modification of SiO2 decrease and those properties of PE fiber EGC specimen after hydrophilic modification of SiO2 improve. In the process of uniaxial tension, most EGC specimens show different degrees of tensile strain hardening, and it is more obvious after the fibers are modified. The results of single fiber pull-out tests show that the EGC specimens have a more obvious slip hardening stage and the interface property of fiber-matrix is improved after fiber surface modification.