In the present paper，two concepts，“defect degree" and “crystallization potential"，are introduced for evaluating the defects in crystal and describing the potential field near the crystal surfaces，respectively. Based on vast MD simulations of Ni，Cu，Al and Ar crystal growth from different faces at various temperatures，it is shown that the defect degree decreases with increasing of the crystallization potential，indicating that the crystallization ability is determined uniquely by the crystallization potential，which can be obtained easily even with ab initio calculations. This result suggests a convenient way to evaluate the ability of materials to form perfect single crystals.