L1251B, which was revealed as a small group of protostars by the Spitzer Space Telescope (SST), presents a great site of studying chemical evolution in gas and ice as well as various dynamical processes associated with star formation (infall, rotation, and outflow). We have mapped L1251B with the Infrared Spectrograph (IRS) aboard the SST to study the chemical distribution in the phases of gas and ice and the dynamical feature related to shock in the region. Various atomic lines and the $H_2$ pure rotational lines, which trace different shock velocities, were detected. In addition, the distribution of the water and $CO_2$ ices hints variety of the ice desorption mechanism in L1251B.