To study the effect of different parameters on milling force for longitudinal torsional ultrasonic vibration milling (LTUM) of titanium alloy, the kinematic theory of LTUM is combined with the model of milling transient cutting thickness to establish the milling force equation, and experiment was carried out. The experimental results showed that: Milling force was positively correlated with cutting speed, cutting depth, feed per tooth (milling force increased by about 40% in increasing the cutting speed from 40m/min to 100m/min, 300% in increasing the depth of cut from 0.1mm to 0.4mm, and 25% in increasing the feed per tooth from 0.01mm to 0.04mm). Milling force was negatively correlated with ultrasonic amplitude, tool helix angle (milling force reduced by about 22% in increasing the ultrasonic amplitude from 1µm to 4µm, and 23% in increasing the tool helix angle from 30° to 45°). The milling force was minimized when the ultrasonic amplitude was 4 µm, cutting speed was 60 m/min, cutting depth was 0.1 mm, feed per tooth was 0.01 mm/z, and tool helix angle was 40°. In further, the empirical model of milling force was established and accuracy was verified by experimental data.