The West Brom head coach believes the Dutchman will be given the time David Moyes never got but needs to get United closer to the top of the Barclays Premier League.
They are fourth in Van Gaal's first season and look set to return to the Champions League after finishing seventh last year.
Van Gaal has ridden out a tough start but Pulis, who takes West Brom to Old Trafford on Saturday, is adamant he needs to deliver next season.
He said: "Louis has obviously spent a bit of money and brought quite a few players in, I think he has had a year to look at it
The difference from himself and (Jose) Mourinho was that Jose knew the league
This is Van Gaal's first season in the league
Next year he has to come close to winning the league, he'll know that
"It's been great experience for him this year
I'm sure he'll add a few players to the squad next year
They'll want to win it, I see them getting stronger, I can't see them getting weaker.
"David didn't get it (time), but Louis has, most probably on the basis he has been successful at bigger clubs
He's won major titles at bigger clubs
He's earned it by what he's done elsewhere, that's a fact of life."
Pulis has a few injury doubts, but refused to name them, although Youssouf Mulumbu is back from suspension.
Source : PA
Source: PA