Abstract: Deformation structure induced by indentation in GaAs single crystal has been studied using transmission electron microscopy. The result shows that resettle-like asymmetric dislocations, which consist of elongated-arm dislocations and short-arm ones, and twofold symmetrical twins occurres around indentation. The dislocation configuration formed by the nucleation, movement and interaction of the Frank-Read sources on six slipping planes of the GaAs crystal, and is closely related to the various mobility of the α and β dislocations in GaAs crystal. The formation of the twins is closely related to the stacking_faults.