Abstract: The laser multispectral detection is an important development direction of laser technology, belongs to active detection technology, and exhibits higher precision than the former passive detection. Aiming at the demand of laser-based multispectral detection for multicolor laser source, a method using spectral beam combining technique in an external cavity to obtain the multispectral laser is proposed. The experimental results of spectral beam combination for two fiber lasers taking large-mode-area Er3+/Yb3+ co-doped double-cladding fiber as the gain medium in an external cavity are reported. Tunable dual-spectrum lasers with 29.3nm and 11.52nm 3dB linewidth were obtained. Experimental results and theoretical analysis show that spectral beam combination in an external cavity is a feasible approach for obtaining the multispectral laser sources.