The configuration of a corium pool in the lower plenum of reactor vessel is very important for validity of maintaining reactor vessel integrity under IVRERVC (In-Vessel corium Retention through External Reactor Vessel Cooling) condition. A method is designed to predict the configuration of corium pool for an Advanced China PWR, call ACP1000 after entire melt dropping into the lower plenum. It takes into account both thermo-chemical reaction of oxides and metals in corium and the influence of different paths of corium relocated from core region into the lower plenum. The reasons why a three-layer pool has not been observed in the MASCA and COSMOS tests are given by this method. The method is applied to investigate the corium configuration of ACP1000 after a hypothetical station blackout (SBO) accident. It is shown that the stratification of the corium pool is related to the relocation paths of the corium. In the case of downward relocation, a two-layer melt pool with a metal layer on the top is formed. For the sideward relocation, the configuration shows a stratified pool consisting of a dense metal layer on the bottom, an oxide layer in the middle and a light metal layer on the top.