Based on the poor plasticity and high temperature required for forming of titanium alloy sheet, an ultrasonic vibration-assisted forming method under thermal conditions was proposed, which is expected to further improve the formability of titanium alloy sheets under thermal conditions. The effects of ultrasonic vibration process parameters on the engineering stress-strain curve, yield strength and elongation of titanium alloy sheet were analyzed by tensile test of TC4 sheet at 200-600℃. And the microstructure and fractography of the tensile specimens were analyzed. The results showed that superimposing ultrasonic vibration process with appropriate parameters in the thermal tensile process can further reduce the flow stress and yield strength of TC4 sheet and improve the elongation, and it can achieve the purpose of further improving the formability under thermal conditions.