Based on the empirical electron theory of solids and molecules(EET), the valence electron structures(VESs) of TiB and TiB2 were calculated, and then the relationship between their VESs and boronizing layer hardening of TC4 alloy was analyzed. The B-B bonds of TiB and TiB2 on boronizing layer are the strongest, and they are far bigger than that of the strongest bond of the substrate. The strongest bond of TiB2 (=0.555 4) is stronger than that of TiB (=0.404 2), so the strengthening effect of TiB2 on substrate is stronger. From the number of atom state group of phases σN, we can know that the stability of TiB2 is far bigger than that of TiB. The space distribution of the covalence bonds decides that it is easy for TiB to grow along the [010] direction and form short threadiness, while for TiB2 it is easy to form high symmetry granulous or globular shape, therefore TiB2 is better than TiB at substrate hardening and the improvement of wear-resisting. From the forming-bond ability of phases F, we can know that the amount of TiB is more than that of TiB2 on the boronizing layer.