A model based on the phase field method is developed to analyze the interface stability during molten zirconium oxidative solidification. This model is capable of capturing the interfacial growth, the solute redistribution, and the flow and heat transfer. The model is validated using zirconium crystal growth experiments. The results obtained from the simulation of the relationship between the growth rate of dendrite tips are compared with the experimentally fitted curves, and the simulation results are in good agreement with the experimental results. The growth process of molten zirconium oxide solidification layer was simulated using the developed model, which successfully simulated the transition from stable to unstable interfaces. The simulation results show that the stability of the interface during the oxidative solidification of molten zirconium is affected by the interfacial perturbation, and the interface tends to become unstable when the intensity of the interfacial perturbation increases with time.