After victories over Stevenage and Dorking Wanderers in the First and Second Round of the competition, the U's will travel to take on Championship Watford for their next encounter.
The game will take place on the 9th December, and will be played at St Albans City FC with a 7pm kick-off.
Liam Bailey's side are yet to play at home in the tournament so far.
In their First Round game they overcame Stevenage 4-1 at the Lamex Stadium with goals coming from Samson Tovide (pictured above), and Harvey Sayer netting a brace each.
And they booked their place in the Third Round with a 2-0 win against Dorking Wanderers last week, with Tom Stagg bagging both goals for the U's in that fixture.
The young U's will be hoping their good form can continute in the FA Youth Cup, as they hope to make it to the fourth round for the first time since the 2017/18 season when they made it all the way to the quarter-finals before losing out to Arsenal.