Abstract: An adjoint-based adaptation sensor is studied in this paper,which is constructed from the so-called adjoint equation of flow field.It is implemented and used to establish an adjoint-based unstructured mesh adaptation method for Euler flow,coupling the h-refinement method for generation of the adaptive mesh.For viscous flow,a completely new strategy is proposed,where the adjoint-based adaptation method is firstly used for Euler calculation to get an initial unstructured mesh with good resolution,and then a hybrid mesh is generated using advancing layer from the adapted mesh.Transonic flow over a two-dimensional RAE2822 airfoil and a three-dimensional ONERA-M6 wing is used to validate the adjoint-based mesh adaptation method,and the complex vortical flow field over a 65° delta wing at high angle of attack from the second International Vortex Flow Experiment（VFE-2）,both for inviscid and viscous cases,is simulated.The numerical results show that the adjoint-based adaptation method presented here for unstructured mesh is feasible and effective.