A mathematical model was set up to calculate the saturated vapor pressure of components in TC4 alloys during electron beam cold hearth melting (EBCHM). The saturated vapor pressure and evaporation rate of components in TC4 alloy were calculated by this model, whose results basically agree with the experiment results. The calculation result shows that at the same temperature the saturated vapor pressure of Al is the biggest, about hundreds of times as large as others, and the evaporation loss is also the most serious. With the increase of the melt temperature, the evaporation trend increases. The evaporation loss of V is very little, which can be neglected. Moreover, electron beam cold hearth melting has the prominent effect in removing inclusions, and it can produce the slabs achieving the national standard.