Abstract: In this paper the measured and calculated results of side-wall boundary layers of dry runs in Northwestern Polytechnical University 100 by 300 mm transonic wind tunnel with solid sidewall and with suctions at sidewall around model are discussed. The axial Mach number distribution in the dry runs, and the effects of sidewall suction against the chordwise and spanwise pressure distributions on a pressure testing model are also analised.It is found that suctions on the sidewall around the model can change the uniformity of the flow field in the dry runs; and by comparing with the solid sidewall, suctions on the sidewall around the model makes spanwise pressure distribution uniform, but change the chordwise pressure distribution on the central section.