A thick snow band often forms along the Okhotsk Sea coast of Hokkaido Island, northern part of Japan. Numerical simulations were made to investigate the formation and maintenance mechanisms of a long-lasted snow band appeared on 26th of December 2008 using Weather Research and Forecasting Model (WRF). The snow band was simulated along the coast of Hokkaido Island, moved offshore toward the Sea of Okhotsk, where it intensified, and was sustained for one and a half days. The results show that Sakhalin Island plays an important role in the maintenance of a convergence line and thus the snow band. Cold air advection from Sakhalin Island produces a strip of warm air between the advected cold air and Hokkaido Island and thus controls the location of the snow band, while topographic blocking by Sakhalin creates the lower level convergence at the Soya Strait and hence enhances the snow band. Temperature and surface-roughness contrast between Hokkaido Island and the Sea of Okhotsk appear to be also important for the initial formation of the snow band.