Abstract: The steady flow fields of the Ф1 m hypersonic wind tunnel are simulated under Mach number 3 and 6 by solving axisymmetric N-S equations.The comparison between the nu-merical simulation and experimental data validates that this numerical method is feasible.And then the flowfields of wind tunnels with closed straight round and unclosed free-jet test sections under these Mach numbers are simulated respectively.The results of uniformity test core of closed straight round and unclosed free-jet test sections meet the requirement of relevant stand-ards.The results show that the minimum diameter of the uniformity test core in Mach 3 nozzle with closed test section reaches Φ882mm at the axial coordinate from-300mm to 900mm.The test core increases by about 31.57% compared with free-jet test section,which significantly im-proves the test capacity of wind tunnel.For Mach 6 nozzle with closed test section,the uniformi-ty test core only increases by about 8.24% compared with unclosed test section,which makes lit-tle improvement on the flowfield performance.The uniformity test core of supersonic wind tun-nel with closed test section enlarges observably,but it is little larger in hypersonic wind tunnel with closed test section than that with unclosed free-jet test section.