Abstract: The pressure gradient has been measured by authors using graphite which is widely applied to diamond synthesis instead of traditional material silver chloride. The pressure gradient in graphite pressure chamber increases with the pressure. The axial pressure gradient is 21.8 MPa/mm and the radial one is 18.8 MPa/mm when the chamber center is at the pressure of 5.5 GPa. It has been also found the pressure gradients in the axial direction and radial direction are almost same at low pressure, but the difference becomes remarkable with increasing pressure. On the other hand, the pressure gradient in silver chloride chamber decreases with the increasing pressure. Some investigations were carried out on the relative pressure gradient, and we found it decreases as the pressure increases. When center pressure is 5.5 GPa, the axial relative pressure gradient is 0.003 96 mm-1 and the radial is 0.003 48 mm-1 . It is suggested that the temperature field could be reasonably designed by taking account of relative pressure gradient.