The report by UNESCO and the International Council on Monuments and Sites recognised the benefits the 1.8m (2.9km) project.
In 2014 the government announced it would commit to building a tunnel, removing the A303 from the landscape.
Historic England, the National Trust and English Heritage also support the plans.
The report highlighted the scheme's potential to become a "best practice case" for a World Heritage Site.
It said the scheme must "both protect the outstanding universal value" of the site and also "benefit road users".
At the moment the congested A303 cuts through the middle of the area.
Helen Ghosh, director general of the National Trust, said the report "recognises the unmissable opportunity" the government's road improvement scheme offers to address "the blight of the existing A303".
Duncan Wilson, chief executive of Historic England, welcomed the report but said "sensitive design" would be needed.
Kate Mavor, chief executive of English Heritage, added: "Provided that it is designed and built in the right way, a tunnel would reunite the wider landscape around the ancient stones, helping people to better understand and enjoy them."
Plans to build a tunnel under Stonehenge have been welcomed in an influential report.