Australia are currently overwhelming favourites to back up their recent Ashes victory with a seventh world title in the 50 over format.
However, England have shown good form in warm-up games and enjoyed a 109-run rout of Bangladesh before beating South Africa by six wickets.
Beaumont, who was the player of the tournament in 2017 as England won the final, believes the defending champions shouldn't be underestimated.
The 30-year-old said: "I feel a lot of people have written us off. Last time people were trying to call us favourites. We are still the holders of the World Cup and you write us off at your peril.
"It would be a massive achievement particularly to go back-to-back. Away from home is always difficult but the conditions in New Zealand are actually quite similar so it's a nice one to try to go back-to-back on.
"Winning a World Cup at any time is a massive achievement but particularly when we have gone through Covid and all the bubbles, restrictions, all that.
"To come out here and hopefully perform would be good testament to the team."
England's first match of the tournament is against bookies favourites Australia on Saturday.
The fixture offers England a chance to avenge their 12-4 Ashes defeat - a series which saw the Aussies claim all three ODI internationals.
However, the result of the opening match might not be as consequential as some might suggest. The defending world champions lost their first match in 2017 against India before going on to lift the trophy.
Beaumont, who topped the run charts with 410 five years ago, is not placing too much emphasis on the showdown with Australia.
She said: "We will take on Australia, on our day we can beat them. We are in a good place for that game, regardless of the Ashes results.
"I don't think one game will ruin your World Cup hopes. It's a good time to get back out there and give it a good crack.
"I didn't have the best series with the bat in the Ashes. But everyone has to step up and we have had some chats, not just about what we want to do but how we are going to do it. We want to play aggressive cricket, taking the game on."
The tournament gets underway on Friday, March 4 as hosts New Zealand take on the West Indies.