Abstract: The application of the continuous adjoint method has been conducted on a 2D hypersonic inlet design optimization. The 2D hypersonic inlet is an inviscid curved compression configuration designed based on characteristics method. The external compression surface has been parameterized through the free form deformation (FFD) method. The viscous mass flow rate of the inlet has been taken as the optimization objective. The flow governing equations and the continuous adjoint equations have been solved on three different grids to analyze the external compression surface sensitivity contrastively. The results indicate that the external compression surface sensitivity has a strong boundary layer mesh dependence. The objective gradients obtained by the continuous adjoint method are credible according to the comparison with the finite difference method. The BFGS algorithm has been adopted, and the optimization results show that the incident shock wave seals the external flow at the cowl. This behavior increases the inlet mass flow rate by 6.3%, and the integrated performances of the inlet have been promoted. The maximum normal displacement of the external compression surface is 5.6 mm. Based on the optimal results, the adjoint method could be applied successfully in hypersonic inlet design optimizations.