The Otters reached the final after running in 10 tries against a depleted Aberystwyth side.
Five tries came before half-time when Narberth led by 33 points. Scrum-half Adrian Killa scored twice and other tries were scored by lock Chris James, together with wingers Tom Bonnell and Jonathan Morgan.
Fly-half Aled Davies was on target with four conversions.
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The mayhem continued in the second half as replacement number 10 Matthew Davies and centre Steve Martin both scored twice and full-back Sion Brace also joined in the fun with a try.
Aled Davies converted one of the tries and the other four were each converted by centre Nick Jones.
Team manager Robert Lewis said: "It is tough to go to Aberystwyth as it is a long way to travel for a mid-week fixture.
"The boys played exceptionally well. In fairness to Aberystwyth, they stuck at it all the way and you could not fault their commitment. Nevertheless, we had a little too much power, pace and skill for them all round."
He added: "It was a very good run out for the boys in between two league fixtures, but as we got on top in the set pieces Aberystwyth did not get much of the ball.
"In view of the disparity between the teams, we always put them under pressure and we scored some cracking tries.
"The forwards presented us with the ball and the backs went through the moves and generally there was good support work all round.
"It was a very good performance against a committed Aberystwyth team which gave 100 per cent throughout.
"We are delighted to be in the final and we hope that we can put up a good performance in what will be our last competitive match this season."
Narberth fielded: Sion Brace, Tom Bonnell, Nick Jones, Steve Martin, Jonathan Morgan, Aled Davies (Matthew Davies), Adrian Killa, Fifitipuku Faletau, Dan Smith, Justin Hughes (captain), David Ebsworth, Chris James, Gareth Bateman, Jamie Bohata, and John Tennick.