A reception and an exhibition on the history of the Folkestone to Coquelles link will be held at Eurotunnel's terminal in northern France.
Formed of twin railway tunnels and a service tunnel 100 metres below sea level, it is considered to be the 20th Century's most important construction project.
The 31-mile tunnel has become a key part of Britain's infrastructure after the Queen and France's then president Francois Mitterrand inaugurated it on May 6, 1994.
Geoff French, president of the Institution of Civil Engineers, said: "The Channel Tunnel is a feat of engineering. It contains one of the longest segments of undersea tunnel in the world, established the first fixed link from England to Europe, and over 13,000 workers from England and France collaborated to realise the vision."
Operations leader Christine Marsh, 60, of Dover, has worked at the tunnel since it opened and told of that time.
She said: "It was quiet back then, everything was so new and exciting. We had to do a lot of training to face the challenges. I was here when the Queen visited. We all knew it was going to be a big thing and that we were part of something new."