The problem of complex and various ingot moulds has bothered special steel enterprises. Herein, three ingot‐weight‐compatible (IWC) designs are described. The 39 tons mould is adapted to cast at most 45 tons of molten steel. The effect of three IWC designs on shrinkage cavity, porosity and macrosegregation is studied. The simulation is based on a polyphase coupled model for momentum, energy, and mass conservation equations. On the basis of the experimental results and previous literature, the interfacial heat transfer coefficient is established. Through finite difference method (FDM) simulation, the effect of the three IWC designs on the solidification is studied. The predictions of shrinkage porosity and macrosegregation are obtained. With the increase of ingot weight, the shrinkage cavity from the hot top is deeper in the three IWC designs. The Niyama criterion is found to be the condition under G/L0.5 < constant (G and L are the temperature gradient and cooling rate, respectively). With this criterion, the extent of centerline shrinkage porosity is predicted. Subsequently, utilizing the three compatible designs, the simulated results uncover that the centerline shrinkage porosity is serious. In addition, it is significant to note that the macrosegregation shows different characteristics.