Abstract: The aramid fiber insulated tie rod is a key component in the application of UHV power transmission. Based on Darcy's law and continuity equation, a numerical simulation method for vacuum impregnation process of aramid fiber reinforced composites and a porosity prediction model were established to solve the problem of pore defects in the production of UHV aramid fiber insulated tie rod. The formation mechanism of pore defects in aramid fiber composites was investigated by means of micro-CT, and the influence of impregnation temperature, speed, vacuum degree and other technological parameters on the formation of pore defects in insulating tie rod of aramid fiber composites was revealed. The results show that the porosity prediction model is in good agreement with the experimental results and can be used to optimize the vacuum impregnation process. In this paper, the aramid fiber fabric is plain weave structure, and the optimum impregnation temperature, impregnation speed and vacuum degree in the vacuum impregnation process are 50 ℃, 0.381 mm/s and 80 kPa, respectively, which meet the actual engineering requirements.