Free energy change for atoms transferred from liquid on to liquid-solid interface is calculated according to the structural model proposed by Jackson. Relationship among the change in free energy, the fraction of sites on the interface occupied by atoms and the interfacial undercooling is presented. This relationship can be used to judge the possible state that an interface may take, and to predict the corresponding crystal growth mode. For silicon and germanium, the experimentally observed growth mode transition from lateral growth at small undercooling to continuous growth at large undercooling is hardly to be explained by this thermodynamic calculation, which implies that the transition is possibly caused by some dynamic reasons. For nickel, crystallization is carried out only by the continuous mode, which is consistent with the experimental observations.