In order to study effect of pulse current frequency on microstructure and mechanical properties of TC4 titanium alloys with prefabricated defects, TC4 specimens with void defects were firstly prepared by pre-stretching at room temperature and then treated by pulse current with different frequencies. Microstructural variations of void and matrix before and after pulse current treatment were compared. Mechanical properties were obtained by second room-temperature tension. The results indicate void volume fraction decreases from 2.21% to 0.86% when pulse frequency increases from 0 to 140Hz. Meanwhile, yield strength and ultimate tensile strength rise from 916.7MPa to 990.9MPa and from 951.2MPa to 997.5MPa, respectively. Moreover, the elongation increases by 64.86%. However, void volume fraction increases to 1.99% when pulse frequency increases from 140Hz to 160Hz. At the same time, yield strength and ultimate tensile strength decrease to 975.1MPa and 988.5MPa, separately. The elongation decreases by 37.70%. Void volume fraction almost determines mechanical properties of TC4 alloys with prefabricated defects.