A roller assembly for transporting a substrate includes a step roller and a plurality of first auxiliary rollers. The step roller includes a main roller, and a pair of edge rollers sleeved on the main roller and located on two opposite ends of the main roller, respectively. The plurality of first auxiliary rollers are disposed on two opposite sides of the step roller, respectively. A first film forms a closed loop through the first film being rolled on the plurality of first auxiliary rollers and the step roller cyclically. A method using the same is also provided.