Aiming at the CFD (computational fluid dynamics) calculation of pressure pipeline crack leakage, a CFD crack leakage calculation method that can consider the pressure drop and phase transformation process of fluid was proposed. Based on theoretical analysis and numerical simulation methods, a rectangular narrow crack model was established to achieve transient simulation of the crack leakage process, and the calculation results were verified and analyzed. The results show that the flow characteristics of the leaking fluid conform to the physical laws of the phase change leakage process, and the calculated results agree well with the experimental results, with an average error of less than 15%. The leakage rate per unit area increases with the increase of crack opening displacement, and increases more slowly with the increase of fluid subcooling. The calculation method and analysis results can provide a direct technical reference for the study of pressure pipeline crack leakage rate.