Abstract: In order to study the pressure propagation process in the case of arc discharge fault in the oil chamber of on load tap changers (OLTC), a computational fluid dynamics model was established based on Navier Stokes equations and numerically solved by finite volume method. The calculation results show that after the fault occurs, the pressure wave propagates around in the form of spherical wave. The side wall and bottom position near the fault point reach the pressure peak in about 3ms. The pressure peak at the side wall monitoring point is 3MPa, and that at the bottom monitoring point is 2.8MPa. Since the top relief valve is far from the fault point, the time to reach the peak pressure is 6.3ms and the peak pressure value is 5MPa. Comparing the numerical simulation results with the field test results, the pressure change trend of the two is basically the same, which verifies the reliability of the established mathematical model and the correctness of the numerical simulation method.