In order to recover the vented gas in Tarim Oilfield as much as possible， save energy and reduce air pollution， Tarim Oilfield Company researched reasons of gas venting in natural gas treatment units of Lunnan gas treatment plant and Sangna gas purification plant in Tarim Oilfield in 2008. Relative information was collected at the site and communication was conducted with operating personnel， deeply analyzed were operation conditions of the units and some problems occurring in their operation and analysis results suggest that insufficient treatment capacity of the units and imperfect treatment process result in gas venting. Therefore， enhanced were gas gathering， pressure boost and refrigeration capacity of the units and some facilities were extended to perfect gas treatment process， assure proper and safe operation of the units and no gas venting， which shows that enhancing gas treatment capacity of the units is one of the most effective ways for resolving the problem of gas venting.