Numerical simulation is performed on the flow behavior of a bubble rising in a liquid medium at high pressures. In the numerical scheme, a computational fluid dynamics (CFD) method is used to account for the flow characteristics of the continuous liquid phase and the gas phase inside the bubble. The Volume tracking based on the volume-of-fluid (VOF) method is used to describe the free surface motion of gas bubble, and the deformational bubble shapes. Simulations are performed simultaneously for both liquid and gas phases by considering the volume-fraction-weighted averaged properties on the interface. The behavior of a single gas bubble rising in Paratherm NF heat transfer liquid at pressures of 0.1 and 19.4 MPa is simulated and compared with the experimental results obtained in this study. The comparison is satisfactory. The results of the simulation indicate that as the pressure increases, the maximum stable bubble size decreases, which is in conformity with the experimental findings.