To study line-edge roughness (LER), we develop a simulation method for the formation process of line edges based on the mesoscale simulation of the dissipative particle dynamics (DPD) method. We model the development and rinse processes based on the coarse-grained resist polymer model. It is important that the block copolymer in which the soluble and insoluble blocks are bonded exists at the line edge. Though the soluble part of this block copolymer is stretched out in the development process, it shrinks in the rinse process. The shrunken polymers contribute to the formation of line edges, and LER is very influenced by these polymers. Our simulations help to analyze the formation process of line edges based on resist polymer chain dynamics.