Threats include proposals for over 80,000 new houses, new roads, open cast coal mines, airport expansion, golf courses and industrial parks.
These developments would be equivalent to a new town greater than the size of Slough being built over the next twenty years, the CPRE claims.
The publication of the map and briefing paper comes two years after a government pledge to "maintain protection of the green belt", it said.
Communities secretary Eric Pickles announced in July 2012 that he would abolish regional planning, so local people could better protect green belts around towns and cities.
Two years on, the CPRE claims that the level of threat remains.
New national planning policies require local authorities to allocate more than five years' worth of building land for new housing, it says.
In many cases it appears that government planning inspectors are putting pressure on local authorities to allow building in the green belt to meet this requirement.
Government plans to reduce further national planning guidance could lead to ministers no longer scrutinising major proposals for development in the green belt, said the CPRE.
Paul Miner, CPRE senior planning officer, said: "The green belt is the most popular planning policy in England and the envy of the world.
"It helps regenerate our cities and stops them sprawling into rural areas. As a result, no one is ever too far from true, green English countryside.
"In times of economic slowdown, politicians can sometimes be tempted by the false promise of an easy construction boom.
"But destroying the countryside is not the path to lasting economic prosperity.
"Sustainable economic improvement can only come from the sort of urban regeneration that has already done much to rejuvenate many of our largest cities."
Mr Miner said building on the green belt was often justified by claiming there was a shortage of other land for development, such as previously developed 'brownfield' land.
But government figures show that the amount of brownfield land becoming available for re-development was far outstripping the rate at which it is being used.
There was enough brownfield land available for 1.5 million new homes, said Mr Miner.
It was vital that the government stepped in to ensure 'smart growth', which focused investment and development within existing urban areas, rather than on green belt land.
Rather than relying on unrealistically high requirements once imposed by regional plans, local authorities should set housing targets consistent with local need, said Mr Miner.
This would protect the green belt and help regenerate brownfield land
But above all, ministers should stick to their commitments to protect the green belt.
This should include actively monitoring major planning applications in the green belt as well as the proportion of new housing on brownfield sites.
"Ministers have consistently maintained that they value the green belt and want to see it protected," said Mr Miner. "Now is the time to put these words into action."