Abstract: Diode lasers’ advantages, such as long operation life, high electro-optical efficiency and selectable wavelength, make the diode laser be an important part of modern laser field. The output power and beam quality are two key parameters to evaluate the performance of diode lasers. Due to the special structure of diode lasers, the beam quality degrades obviously with the increasing power, which limits diode lasers to be employed as a direct light source. The spectral beam combining technology has been proven to be an effective way to achieve beams with both high power and good beam quality. However, in practical spectral beam combining system, the power and beam quality of combined beams still have a non-negligible degradation, and the issue of how to get beams with high-brightness has been attracting the attention of an increasing number of researchers. In this paper, the diode laser array/stack is introduced briefly, and three kinds of gratings employed in spectral beam combining system are analyzed. The spectral beam combining technique by grating-external cavity is described in detail, and then the development of spectral beam combining technique of high-power diode laser array is briefly reviewed. Factors which make the beam quality deteriorate and the combining power degrade are analyzed in detail. Finally, the future development of high-brightness diode lasers is prospected. This work is expected to promote the further development of spectral beam combining technique by grating-external cavity.