In the QCD, a transition restoring the chiral symmetry occurs at a high temperature and density. Searching for the signals of the QCD phase transition is one of the goals of the current relativistic heavy-ion physics programs. The metastable state is a unique feature of the first-order phase transition. Using the van der Waals equation of state, the role of the metastable state in finite-size effects is analyzed. It is found that the finite-size effects of the first-order phase transition are closely related to the metastable state. Metastability can be observed in the distribution of the orde...