The authors propose a method to simulate the DNA motion in microchannels of complex geometry. It is based on stochastic rotation dynamics using a new scheme for the boundary condition. The method enables them to define a boundary wall of arbitrary shape and to describe a wall moving at an arbitrary velocity. As an application, they simulate the motion of DNA in Poiseuille flow between two parallel planes and show that DNA molecules tend to concentrate near the center of the channel in agreement with experimental results.