As diode laser processing for different processing technologies demands different power densities and spot sizes, this paper researched how to get focus spot outputs with different sizes by adjusting optical path design to meet the requirements of various laser applications. By using ZEMAX to simulate the diode laser optical path, including beam shaping, collimation, focus, etc., several kinds of spot outputs with various sizes was implemented. In the experiment, a 980 nm diode laser stack with the superposition of 16 bars was used by a threshold current of 6.4 A, the maximum operating current of 84.8 A, maximum output power of 1 280 W, and the total electrical-optical conversion efficiency of 58.9%. After collimation, the divergence angles for the fast axis and slow axis are less than 4 mrad and 20 mrad, respectively. Finally, the experiments were performed on the diode laser stack by the beam shaping, collimation and focusing, and a power output of 1 031 W is obtained. Furthermore, the focused spot size has been 1.2 mm × 1.5 mm and the laser power density is up to 3.8×104 W/cm2 when the focal length of focusing mirror is 300 nm. Results show that the laser stack can be used in remelting, alloying, cladding and thermal conductivity-type welding for metal surfaces.