The physical model for a square alloy molten pool heated by an electron gun is described by the Navier-Stokes, energy and species concentration equations. The velocity, temperature and concentration distributions of the two-dimensional pool are analyzed by the finite difference method. The relations between the metal solvent evaporation rate and Rayleigh number Re, Prandtl number Pr, Grashof number Gr and Lewis number are studied in detail. In general, the solvent evaporation rate increases with decreasing Rayleigh number,decreasing Prandtl number, increasing Grashof number and increasing Lewis number, so the power use ratio of the electron gun increases. On this basis, such metal solutes as wolfram, neodymium and chromium is intermingled to such involatile metal solvents as thorium, platinum, ytterbium and ruthenium, and the numerical results indicate that the metal solvent evaporation rate increases.