Abstract: A Central Asian vortex (CAV) of medium-range time scale (over 4 days) is a deep cutoff low in the troposphere, and it is also one of the important influence systems which cause rainstorm, snowstorm and persisting low-temperature in the Xinjiang region. But the energetic characteristics at its formation, maintenance and mature stage are not clear. Energetic characteristics of the medium-range process of CAV during 10-20 July 1996, which caused 2 rainstorm processes in Xinjiang, are investigated using the NCAR/NCEP daily 2.5°×2.5° reanalysis data and the energy cycle equations for open atmospheric region. The results show that distinct features exist for the different periods. This vortex is always getting along with baroclinic instability conditions during either the developing and weakening process. The conversion term from eddy available potential energy (AE) to eddy kinetic energy (KE) and the eddy kinetic energy inflow (BKE) from open atmospheric region boundaries act as main sources of the KE, and they play an equivalent role in bring about the rapid development of vortex, and at the same time a part of eddy available potential energy by the diabatic heating (RE) exports. Since RE is more than AE→KE and BKE, it causes vortex to weaken during the weakening stage. The vortex keeps barotropic instability conditions with weak energy conversions within vortex during its mature stage, and the source and sink of KE is eddy available potential energy import from environment and eddy kinetic energy outflow, respectively. During the every stages the conversion term from the zonal kinetic energy (KZ) to KE is very weak, suggesting that energy conversion from barotropic instability is rather little. KE is quite strong at the middle and upper troposphere, implying that the Central Asian vortex mainly exists about over 700 hPa. Energy conversion within the vortex and energy transportation with environment mostly take place over 700 hPa. AE and KE variation can primely manifest intensity change and the developing stage of vortex. Energy vertical transportation promotes the vortex development to a certain degree.