Abstract: A double wavelength combination and long focal length optical system was designed to combine and focus two direct high power laser diodes stacks with different wavelengths for laser material processing. First of all, the two LD stacks were collimated by fast and slow axis collimator respectively. Second, the two LD stacks were combined by double wavelength combine mirror. Then, the invert Kepler telescope system principle was applied to expand and collimate the laser beam in the slow axis direction. Finally, the fast and slow axis laser beams were focused at the same time. The focus optical system was analyzed by beam parameter product theory, and the focal depth was also be calculated by Rayleigh length formula. The whole optical path was simulated by ZEMAX software, and the simulation results were shown after ray tracing. Based on the theoretical analysis and ZEMAX simulation, the corresponding experiment were performed. After the combination and focusing, the focused spot size was 2.0 mm4.0 mm, and focal length was 300 mm. The final output power was 5 000 W and power density could reach to 104 W/cm2. The influence factors of this optical system were discussed finally. The focused spot can be applied to material processing, such as laser cladding and surface treatment.