The electronic structure of NiSi2 was calculated by using the self-consistent LMTO method. Our result was found to be in resonable agreement with the results of AEUPS photoemission experiment and other calculations. The change in the Ni electron configuration was found to be responsible for the Ni3p3/2 core level binding energy shift; the decrease of Ni3d electrons weakened the screening effect for the Ni3p electrons. The result of calculation showed that the ionicity plays a minor role in chemical bond.