The stable Pickering emulsions were prepared by SiO2 nanoparticles whose surface were combiningd with octyl-grafted amphiphilic alginate derivative(OAAD) hydrophobically modified by 1-Octyl amine. And the properties of OAAD, aqueous dispersion of OAAD/SiO2 nanoparticles and Pickering emulsions were characterized by means of Fourier transform infrared spectroscopy (FTIR),1H nuclear magnetic resonance(1H NMR),Surface tensiometer，fluorescence spectrum，dynamic light scattering，Contact Angle Meter and optical microscope studies. Experimental results showed that Octyl amine groups had successfully grafted to the alginate(SA) molecular chains. The surface tension of modified alginate was lower than SA and the critical aggregation mass concentration was reduced to 0.60g /L，which showed good amphipathy．When the water dispersion system was formed by adsorption of OAAD on the surface of SiO2 nanoparticles and used to prepare stable Pickering emulsions, it was observed that with the increase of OAAD’s mass concentration, the wettability of SiO2 nanoparticles increased, the zeta potential decreased and the particle size increased whereas the particle size of Pickering emulsions decreased that enhance the stability of Pickering emulsions. preliminary analysis of the mechanism, it was indicated that a certain concentration of OAAD adsorbed on the surface of SiO2 nanoparticles could lead to the flocculation among the inter particles, so that the network structure of interfacial film formed in the oil-water interface which was helpful to improve the stability of Pickering emulsions.