Some factors effecting the porosity of porous tungsten, such as powder size, press pressure, sintering temperature, and so on, are discussed in detail. It is found that the porosity of the pressed blank is not only connected with the press pressure, but also with the size of tungsten powder. For the same size of powder, the porosity of the pressed blank decreases with the increase of pressing pressure. The porosity of pressed blank of coarse powder is smaller than that of fine powder for the same pressure. If the sintering temperature and time are the same, the porosity of porous tungsten made by fine powder is smaller than that of the coarse one. For the same size powder, the porosity of the pressed blank decreases with increase of sintering temperature. Therefore, the powder size and sintering temperature are major factors for the porosity of porous tungsten. The smaller the size of the powder and the higher the sintering temperature, the less the porosity of porous tungsten.