Multistage 3D steady and unsteady viscous computations are conducted for a transonic axial compressor with an IGV, rotor and stator blade row. A fully conservative sliding technique is developed with high order shock capturing schemes to better capture the interaction between stationary and rotating blade row. A 1/7th annulus is used for the unsteady simulation with a phase lag BC. For comparison purpose, a steady simulation of the same multistage compressor with single blade passage is performed using the mixing plane approach. It is shown that the sliding BC captures wake propagation very well in the interaction between blade rows. The unsteady multistage simulation using sliding BC and phase lag BC predicts almost identical loading distribution to the steady state simulation at the mid-span, but have significant loading distribution difference at tip section.