Extinction enhancement of GaSb nanowire because of Au nano antenna is studied based on finite difference time domain method. The electric field property and optical property of Au nano antenna array with different shapes are analyzed, it is found that triangular is the best structure, which possesses the resonant absorption peak with high intensity and the electric field with high enhancement factor. Then, the engineering of size and gap with nanowire of triangular structure is performed. Adjusting the triangular size and the gap of nanowire respectively, the results show that the corresponding extinction peak increases from 783 nm to 1638 nm monotonously with the size increasing from 70 nm to 210 nm, and the intensity and enhancement factor of electric field are enhanced. The size of 200 nm is six times the enhancement factor of 70 nm; Increasing the gap from 80 nm to 130 nm, the corresponding extinction peak decreases from 1655 nm to 1460 nm, with lightly weaken intensity and enhancement factor of electric field. So the optimal approach of tuning the size after the determined gap is appeared for the design of Au nano antenna structure.