In order to optimize the properties of fiber-reinforced ordinary Portland cement-sulfoaluminate cement composites (OPC-CSA-ECC) and extend the use of nano-SiO2, this study discussed the effects of nano-SiO2 on the setting time, strength and toughness of OPC-CSA-ECC. Microstructure and modification mechanism of OPC-CSA-ECC were analyzed by XRD and SEM. The results show that, nano-SiO2 shortens the setting time of the composite cementitious, and the greater the content, the shorter the setting time. Nano-SiO2 improves the strength and toughness of OPC-CSA-ECC. The appropriate content of nano-SiO2 is 1.5% (mass fraction), the corresponding compressive strength at 7 d and 28 d is 59.1 MPa and 85.4 MPa, and the equivalent flexural toughness is 195.82 kJ/m3 and 256.51 kJ/m3, respectively. Nano-SiO2 doesn’t change the type of hydration products, but promotes the formation of C-S-H gel and consumes some portlandite crystals. SiO2 increases the adhesion between the matrix and fiber by increasing the density of the matrix, which contributes to improve strain hardening ability.