Considering terrestrial gravity and natural convection of protected gas, a calculated model of minimum temperature of spherical sample under electromagnetic levitation melting is derived. The range of minimum temperature is calculated without regard to the conditions of the heat dissipation by emission in gas. For argon, which has poor cooling ability, the heat dissipation by gas can be neglected in the temperature calulation. For helium, which has strong cooling ability, when the sample has high density, high electrical resistivity and low emissivity, the heat dissipation by gas can be neglected in the temperature calculation, too. When the sample with low density, low electrical resistivity and high emissivity, the heat dissipation by gas must be considered. When sample has high melting point, low electrical resistivity, low density, high emissivity and the gas has high cooling ability, the sample is easy to obtain undercooling under electromagnetic levitation in terrestrial gravity without additional cooling. When levitation melting sample has low melting point, high electrical resistivity, high density, low emissivity and protected gas has poor cooling ability, the sample is difficult to obtain undercoling.