Sympathetic cooling is one of the most promising techniques for producing ultracold molecules from precooled molecules. The previous work has shown that it is inadequate to use the ultracold alkali-metal atoms as coolant for sympathetic cooling. Whether the ultracold alkali-earth-metal atoms can be used as coolant deserves to be investigated. In this paper, the cold collision dynamic behaviors for Mg atom and CO molecule are investigated by quantum scattering calculations. The influences of electric field on the elastic and inelastic collision cross sections of low field seeking state within cold and ultracold temperature are explored. The results show that sympathetic cooling CO molecule with ultracold Mg atom might be difficult to perform.