The Three Lions are overwhelming favourites to retain the urn in the five-match series but the Middlesex paceman is wary of the threat the Baggy Greens can pose.
Finn told Sky Sports News: "I think it would be foolish to underestimate the Aussies. They are always a very competitive team and have got some excellent cricketers.
"We can't allow ourselves to think it is going to be easy, by any stretch of the imagination.
"We know that if we play our best cricket we can win the Ashes but it is going to take a lot of hard work and fight from our side to make sure that happens."
The first Test starts on July 10 at Trent Bridge.