Abstract: Gravimetric method and static expansion method have been used for volume ratios of complicated vacuum vessel. The volume ratios of complicated vacuum vessel can be measured by gas static expansion method,which was mostly developed for the precise measurement of expansion ratios in static expansion systems. At present volume ratios of complicated vacuum vessel were mainly measured in the high pressure. It can reduced the influence of outgassing in the chambers. However,measurements of the volume ratios using the gas expansion methods below 10^-2 Pa are influenced by outgassing from vacuum vessel. We have put forward using the non-evaporable getter (NEG) pumps,which pump active gases but have a few pumping speed for inert gases. we have made use of the inert gases Argon,Helium measuring the volume ratio of complicated vacuum vessel combine with the static expansion method.