Titanium alloy is employed in aerospace, aviation, navigation, and other fields because of its excellent comprehensive properties, such as high specific strength, strong heat resistance, excellent corrosion resistance, and good low temperature performance. However the high cost of titanium alloy seriously restricts its large-scale application. Based on Ti-6Al-4V alloy which has the best comprehensive properties, several Ti-Al-V-Fe alloys with different contents of V and Fe were designed under the guideline of using cheap alloy elements instead of expensive alloy elements. With the help of the stability factor K_β, the stability of β phase and the effect of β stabilizing elements were analyzed. The calculation models for critical cell coefficients ofβstabilizing elements of quenched alloys and annealed alloys were established by theoretical derivation. On this basis, the calculation methods for volume fraction of α phase and β phase were established, and the theoretical calculation of the volume fraction of α phase and β phase in Ti-Al-V-Fe alloy was realized. Taking Ti-6Al-3V-1Fe alloy as an example, the theoretical volume fraction of α phase and β phase in the alloy was calculated. Then, Ti-6Al-3V-1Fe alloy ingots were prepared by vacuum non-consumable arc melting furnace. Samples were taken and heat treated. Finally, the volume fraction of α phase and β phase in the alloy was determined by X-ray diffraction. It was found that the measured results were in good agreement with the theoretical calculation results, indicating that the established model is feasible to predict the volume fraction of α phase and β phase.