Rubber powder（RP）was used to replace part of fine aggregates to produce rubberized cementitious composites (RCC) and the effect of RP volume fraction on degradation of RCC compressive strength was investigated. Then, nano SiO2 (NS) was added into RCC for further modification, combined with capillary water absorption test and microstructure analysis, the enhancement mechanism of NS on RCC was revealed. The results show that after mixing with RP, the compressive ductility of RCC increases, while the decline rate of compressive strength with the increase of RP volume fraction shows three stages and RP especially retards the early age growth of RCC strength. After the addition of 1%(by mass) NS, the compressive strength of RCC specimens with 5% and 10% rubber powder increases by 198% and 181% respectively, while the capillary water absorption coefficient decreases by 289% and 306% respectively. The results of ESEM test and energy spectrum analysis show that the defects in the interfacial transition zone of the rubber powder after adding NS are reduced, and the internal pore structure of RCC is refined. Meanwhile, masses of low calcium silicon ratio C S H gel phase are generated.