The preliminary results of scanning transmission electron microscope investigations on the interface of GaInAsSb/GaSb heterostructure were presented. STEM images show that the various dislocations and stacking faults were produced by the lattice mismatch between the quatary GaInAsSb alloy and GaSb substrates. All these defects were the ways for relieving the misfit strain, including 60° dislocation, 90° dislocation and stacking faults. It is also found that only the 90° dislocation can form the ridges on the surface of the epilayer.