Abstract: To research the ways of relieving inlet unstart phenomenon,the flow of a typical hypersonic 2-D inlet with different suction positions was analyzed in this paper.The result shows that,the inlet with suction can start easily,but the position of suction decides the impact.In the presence of suction in internal passage,the starting ability improves obviously with the growing suction flow,and the phenomenon is more obvious.The start ability improves finitely in the presence of suction in external pressure surface.The flow of suction can adjust with flow Mach number where suction with pressure changes largely before throat,and the start ability can be improved markedly.The impact on aerodynamic performance is that,the pressure efficiency increases with suction in external pressure surface,but declines with suction in internal passage and isolator.