Abstract: This paper investigated the effects of the degree of sidewall shade on the performance of a two-dimentional mixed-compression rectangular cross-section inlet designed for Ma_d =2.4 working in Ma_∞=2.51 and 2.27 of non-sideslip flight condition.The relationships between inlet performance parameters at throat and sidewall shade were obtained,and the reasons of these changes were analyzed.The results indicate that,the performance parameters will change obviously when the bottom of the sidewall is located after the flat compression surface.For the two-dimentional mixed-compression inlet of this paper,when the back positioned sidewall is adopted,the starting performance will be improved while significantly increasing the drag and reducing the flow coefficient.