In order to obtain the wall pressure distribution of large aspect ratio airplane’s wind tunnel experiment with variable Mach number and wing span, guideline of the large airplane’s wing span design is provided in high speed wind tunnel, a large airplane model with variable wing span is designed and the wall interference experiment is conducted in 2.4 m transonic wind tunnel. The wall pressure distribution is measured with 13 tubes in test section, while the Mach number ranges from 0.4 to 0.86. The ratio of model’s wing span and the test section’s width ranges from 65% to 90%. Results show that wall pressure would change suddenly when the wing span is larger than the critical value (70% width of test section) in subsonic, while the transonic results remain unchanged. The wing span of large aspect ratio airplane in the subsonic wind tunnel must be restricted while the transonic test model could be designed larger.