The game on July 31 will bring back memories of the last clash between the two sides in July 2006 when Watford were 3-2 winners on Paul Lambert's managerial debut in Buckinghamshire.
It will also provide a chance for Blues duo Marvin McCoy and Joel Grant to come up against the club where they began their careers.
"I'm delighted that we've been able to arrange a game with a side of Watford's quality," Wycombe boss Waddock told the club's official website. "It's a good fixture in our pre-season programme and it will test the players' fitness levels against a Championship team."
Meanwhile, Waddock's men will travel to Staines Town for the second summer running on July 21.
The Blues cruised to a 5-0 success at Wheatsheaf Park last year thanks to goals from Matt McClure (2), Stuart Beavon, Jesse Kewley-Graham
and Jordon Ibe, who has since signed for Liverpool.