New Guanjiao Tunnel [1](Chinese: 新关角隧道; pinyin: Xīn Guānjiǎo Suìdào) is a tunnel on the 2nd line of Qinghai–Tibet Railway in Guanjiao Mountain, Qinghai province.

The total length of the tunnel is 32.645 km (20.285 mi), which made it at the time of completion the longest railway tunnel in China and fourth-longest in the world.

The New Guanjiao Tunnel was designed for two parallel single-track tunnels with speeds of up to 160 kilometres per hour (99 mph).

The total construction duration was projected to be 5 years.

The tunnel was bored in difficult geological conditions and high altitude, exceeding 3,300 metres (10,800 ft) above sea level.