The effects of B addition on the lattice constant, grain size and electrical property of Al-Si casting alloys were investigated by Wheatstone Bridge Conductivity Measurement, Optical Microscope, Scanning Electron Microscope(SEM), Transmission Electron Microscope(TEM),X-Ray Diffraction(XRD) and Electron Probe Micro-Analyzer(EPMA) Analysis. The results indicated that impurities of Ti,Cr,Mn,V were converted from solid solution state to boride in the Al matrix when B content was increased in the range of 0.02%, meanwhile, the degree of lattice distortion decreased which resulted in the increase of the conductivity by 6.06%; When B content was over 0.02%, B and Ti formed TiB_2, TiB₂ promoted the formation of Al₃Ti phase with the increase of B content, which led to grain refinement, crystal distortion increased, the risk of electron scattering enhanced and the excessing of B dissolved in the Al matrix simultaneously, so the conductivity decreased by 2.5%; when B content was 0.02%, the alloy’s electrical property achieved the best and the tensile strength have not reduced, the conductivity was 33.00%IACS.