The spectral beam combining with an array of high-power and high-efficiency diode lasers is reported by using a common external cavity which contains a transmission grating, while simultaneously forces each element to operate at different, but controlled wavelengths and forces the beams from all the elements to overlap and propagate in the same direction. Using the diode laser array with front-mirror surfaces coating with high transmittance films, a continuous-wave laser with output power of 52.2 W and electro-optical conversion efficiency of 47.9% is achieved. The spectral linewidth is about 15.17 nm. Beam parameter product (BBP) is 3.7 mm·mrad, which is the same as that of single element of the array.