The external cavity-based spectral beam combining of Er3+/Yb3+ codoped fiber lasers is studied experimentally by using laser diodes as pump sources and large-mode-area Er3+/Yb3+ codoped double-clad fiber lasers as the gain media. The external cavity is composed of a blazed grating, a Fourier transform lens and an output coupling mirror. With the external cavity, single fiber laser can produce wavelength-tunable output. The tunable range is 38 nm and the linewidth is less than 0.08 nm. Spectral beam combining of three fiber lasers is performed. The combined output power is 940 mW with the combining efficiency of 74.3%. The output beam profile is stable with good beam quality and the beam quality factor M2x in the horizontal direction is 1.320, slightly higher than that of individual laser output which is 1.204. When using Fourier transform lens with longer focal length, the combining potential of the system can be increased and the beam quality can be improved.