It will prevent light aircraft flying over the area below 10,000 ft (3,048 m) between the 3-5 September.
The Civil Aviation Authority (CAA) imposed the restriction following a request from police.
The ban will not affect emergency services, or commercial flights travelling to and from Cardiff and Bristol airports.
In an advisory sent out to pilots, the CAA said the restriction was part of the security operation being put in place to protect heads of state, including President Barack Obama, who are attending.
Unauthorised aircraft will not be able to fly over the area from Newport, Cardiff and the Gwent valleys, to Ross-On-Wye, Bristol and Minehead.
Flights which breach the ban will be intercepted by police air support.

The 16ft (5m) beard statue - a "symbol of wisdom and learning" - will stand on the University of Salford's campus.
Arts company Engine, who are behind the piece, said the idea came from a 1980s plan to relocate an Eastern Bloc statue of the thinker to Manchester.
Engels, who wrote The Communist Manifesto with Karl Marx, lived in the area from the 1840s onwards.
The sculpture will depict the nose and whiskers of the father of Marxist theory and be situated on the university's Peel Park campus in 2016,
It features a climbing wall at the front, stairs to the rear and a viewing platform at the top, from which climbers can admire the view across Salford.
Engine's Jai Redman said the work used Engels' "signature magnificent beard as a symbol of wisdom and learning", while the climbing aspect came from a desire to make it an "interactive piece".
"We're aren't interested in making 'a hero on horseback', [which is] something Engels would have been horrified by.
"Engels' Beard is a metaphor for how it is an effort and a struggle to pull ourselves out of ignorance [and] a direct representation of how all philosophers 'stand on the shoulders of giants'."
Source: Encyclopaedia Britannica
He said Engels had been chosen as "a great socialist, thinker and a philosopher, a local historical figure and a champion of the working classes", who dealt with issues still "alive and real" today.
"There is a huge issue in Salford and Manchester, where wage inequality and mass poverty is being seen on levels not experienced here since Engels' time."
The idea had come from an "audacious" plan to relocate a statue of the thinker to nearby Castlefield Basin in the mid-1980s, which "attracted broad support, but failed to materialise when no suitable sculpture could be found", he said.
The plan was documented in former Hacienda DJ Dave Haslam's book, Manchester, England, where Redman first saw it.
He said that ever since, he had been waiting for "a good opportunity" to create the statue.
Haslam said the climbing wall was "bizarre and hilarious" but appropriate as "we should not be precious about Engels".
"Engels had a sense of fun. He used to go drinking in Manchester," he said.
"Landlords knew him and his friends, and he'd play jokes and get into scrapes."
The University of Salford's art curator Lindsay Taylor said she was "delighted that even before work has begun on Engels' Beard, it has engaged public imagination".
"All great art should provoke and encourage debate. It is entirely appropriate for the university as a place of learning to be involved with commissioning new art on educational subjects."
Engine said there were no plans to create an accompanying Karl Marx beard sculpture, but added they were "approaching authorities in Germany to perhaps site the other side of his face in Munich".
A no-fly zone has been put in place for parts of south Wales and Bristol during the three-days of the Nato summit.
[NEXT_CONCEPT]
The "magnificent" beard of socialist thinker Friedrich Engels has inspired a climbing wall sculpture in Salford.