The world champions eased to a 2-0 victory in Lille on Sunday thanks to Shkodran Mustafi's first international goal and an injury-time strike from substitute Bastian Schweinsteiger.
Low's side therefore lead Poland on goal difference after their neighbours beat Northern Ireland 1-0.
But the head coach, who saw Germany lose 2-0 in Warsaw in qualifying for the tournament, knows his team will need to be better when they meet Poland in Paris on Thursday.
"We have both won, so the game is really important for the future of the group," Low said.
"I think we will really have to put in some work.
"Poland are in any case a strong team. We've played them twice and of course we lost once.
"With [Robert] Lewandowski they are strong in attack. Like Ukraine a little, they have dangerous players going forward."