A spokesman for Eurotunnel in France said paramedics were called after the boy obviously still in his teens, was found unconscious near the railway tracks on Wednesday night.
He is the 11th person to have died in or near the tunnel while trying to reach Britain since late June.
In recent weeks there has been a fall in intrusion attempts at Eurotunnel's Calais terminal, following the introduction of new security measures.
Eurotunnel has said migrants are making about 150 attempts to get into the terminal each night, down from a high of about 2,000 earlier in the year.
Last week a man died after being electrocuted a man died at the entrance to the Eurotunnel in Calais. He was found on the roof of a freight train.
The situation in Calais is part of a wider migrant crisis across Europe, with huge numbers of people heading north from the Mediterranean.
On Wednesday European Union leaders pledged another one billion euros (£700m, $1.1bn) to help UN agencies support Syrian refugees in the Middle East, as part of renewed efforts to tackle the crisis.
