The graves are lined with wooden planks and were found to contain coffins made from hollowed-out tree trunks.
Experts also found a structure thought to be one of the first churches built in this country at the site in Great Ryburgh.
It was discovered in an excavation carried out ahead of a scheme to create a wildlife lake and flood defence system.
It is the first time such "exceptionally" well-preserved Anglo-Saxon wooden graves dating from the 7th to 9th centuries have been found in Britain.
Anglo-Saxon coffins rarely survive because the wood rots, and previous evidence of burials has largely consisted of staining in the ground from decayed wood.
But waterlogged conditions in the Wensum river valley, with a combination of acidic sand and alkaline water, were perfect for the skeletons and wooden graves to survive, experts said.
They found 81 coffins at the site which is believed to be the earliest examples of a Christian burial found in the country.
Experts found a timber structure thought to be a rare example of an early church or chapel, as well as wooden grave markers, east-west alignment of graves and a lack of grave goods which would be expected in a pagan site.
Duncan Wilson, chief executive of Historic England, said: "These rare and exceptionally well-preserved graves are a significant discovery which will advance our understanding of Middle-Saxon religious beliefs and rural communities.
"This cemetery has been revealed because under the current system, archaeological surveys are required before work on a sensitive site starts.
"This site has immense potential for revealing the story of the community who once lived there."
