The DC volume resistivity and high field conductivity of nano-Ag/epoxy resin polymer composite were researched. The results show after trace addition of Ag nanoparticles with small sizes, the composite has obviously higher volume resistivity than pure epoxy resin. The increase of resistivity is relative with Ag particle size, adding content and characteristics of base polymer. High field conductivity tests show that the coulomb blockade effect appears when Ag particles of small size disperse evenly in the polymer, i.e. the transmission of electron charge can be restricted by nanoparticles. When the adding content of Ag nanoparticles is too much or their size is too big, the composite shows space charge limited current property. TSC results show that more deep traps exist at the interface between nano Ag and polymer, which causes space charge limited current for charge captured and escaped from the traps