Abstract: Tension-unloading-compression and compression-unloading-tension tests are carried out to study the influence of pre-strain on the deformation behavior of TC4ELI titanium alloy. The results show that TC4ELI titanium alloy exhibits obvious bauschinger effect in both the tensile-first and compressive-first tests. With the increasing of pre-strain, the reverse yield strength decreases first and then tends to be stable. The saturated pre-strain under pre-tension test is about 2%, and the saturated pre-strain under pre-compressive test is about 4%. The reduction of yield strength is more obvious after pre-compression. The non-uniform plastic deformation due to the crystal orientation differences and highly asymmetric close hexagonal structure of α phase contributes to the residual stress, which is the main cause for the bauschinger effect in TC4ELI titanium alloy.