Qinling tunnel of HanjiangWeihe Water Transfer Project is a single tube tunnel. An inclined shaft is installed to facilitate the construction of the main tunnel. After the excavation of the inclined shaft reaches the main tunnel, the tunnel will be excavated in both directions. The maximum singleheading ventilation length of the tunnel reaches 6 386 m. Due to the restraints of having such a ventilation length in a small crosssection of the main tunnel, together with issues of synchronous lining, the number of passing vehicles and the size of the ventilation pipes, the conventional ventilation methods, if adopted, cannot meet the requirements of the tunnel construction. Therefore, relay ventilation using small plenum is proposed. Air supply calculation is carried out to verify the feasibility of the relay ventilation proposal. As a result, the construction procedure is optimized with the assistance of the ventilation measures, and the ventilation system is consequently optimized. Finally, field measuring is taken, which indicates that the relay ventilation system adopted has achieved good result. The paper provides reference for similar projects in the future.