The 22-year-old Briton last month became the first driver in the sport's history to finish his first three races on the podium and is likely to be a winner before the season is out.
"I think he's doing a very good job," said Schumacher, attending his first grand prix since retiring as a Ferrari driver last October.
"It's not a surprise to me after seeing his races last year in particular," added the German. Hamilton won the GP2 support series in 2006.
"It may be a surprise that he is so consistent, but there you go. He's well prepared, he's quick and he does the job."
Hamilton lapped fastest in Friday's first practice for Sunday's race at the Circuit de Catalunya, a home race for his double world champion team mate Fernando Alonso.
The Briton finished third on his debut in Australia and followed that up with second place in Malaysia, behind Alonso.
He then beat the Spaniard in the last race in Bahrain, taking second place behind Ferrari's Brazilian Felipe Massa.
Barcelona is the first circuit that Hamilton knows well, from testing and racing there in GP2, and he has refused to rule out victory on Sunday despite most of the sell-out crowd supporting his team mate.
Alonso, Ferrari's Kimi Raikkonen and Hamilton are locked in a three-way tie on 22 points at the top of the standings with McLaren leading Ferrari by five points in the constructors' championship.
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