Six years after Beijing spent $3.5 billion to build what was then the world’s largest airport passenger terminal, China's national planning agency has green-lit a new airport that will cost nearly four times as much.

On Monday, China's National Development and Reform Commission announced it had approved the construction of a new airport in the southern Beijing suburbs to ease congestion and overcrowding at Beijing International Airport. The new airport, which will be designed by Netherlands Airport Consultants, is expected...