In the present study, Effect of Al element addition (1~3wt.%) and heat treatment on microstructure evolution and mechanical property of one new alloy Ti-xAl-3.5Fe-0.1B was studied. Results indicated that Ti-xAl-3.5Fe-0.1B is α+β two-phase titanium alloy. Yield strength of the alloy increased from 590MPa to 900MPa and tensile strength increased from 808MPa to 1074 MPa with the variation of Al element from 1% to 3% due to solid solution strengthening effect, at the same time, the elongation to failure reduced to 15.4%. Microstructure observation revealed that the thickness of the lamellar primary α phase reduced and the grain size remarkably refined as the increasing Al element content. Meanwhile, It was found that yield strength continuously increased to 1000 MPa, tensile strength increased to 1144 MPa and the elongation to failure increased to 17.5% separately after double annealing, which indicated unique mechanical property. The metastable β phase formed in the microstructure decomposed to secondary α phase with fine grain size during the double annealing in the alloy, which blocked the movement of dislocation and induced enhancement of strength, at the same time, the dispersion of secondary α phase on β substrate was also beneficial to the strength. On the other hand, the present of equiaxed α phase was considered favorable to the improvement of elongation to failure.