Based on the empirical electron theory of solids and molecules（EET）

the valence electron structures（VES）of solid solution was calculated and the mechanism of alloy elements of titanium alloy was analyzed from valence electron view.It is shown that the bigger the share electron pairs nAin the strongest valence band

the more the solution strengthening effect of alloy element of solid solution.The bigger nAis

the more difficult for the strongest band to be broken up

the lower the solid phase transition temperature ofα/（α+β）.The bigger the covalence electron densityρc

the more stable solid solution

and the more the effect of alloy element onα/（α+β）phase transition

the lower the phase transition temperature.The biggerρcis

the smaller nAis

the narrower the（α+β）two-phase region of solid solution.On the contrary

with the decrease ofρc

nAis increased

so the（α+β）two-phase region is enlarged.