In order to study the mode characteristics of the external cavity diode laser array spectral-beam-combined system, based on rate equation of the optical feedback diode laser, the coupled cavity oscillating model of the diode laser emitter is established, and the condition of modes that can stably oscillate in the coupled cavity are given, and the oscillation modes that satisfy the phase condition are divided into single mode oscillation (only one mode can stably oscillate in the coupled cavity) and multi-mode oscillation (multiple modes can stably oscillate in the coupled cavity). Combined with the gain curve of the coupled cavity, the mode structures and beam properties of single mode oscillation and multi-mode oscillation are given, and the effects of the structural parameters of the spectral beam combining system on the mode stability are analyzed. The results show that enhancing the reflectivity of the laser′s front surface and reducing the external cavity′s equivalent reflectivity can enhance the spectral combining light source′s modal stability. For arrays with a larger number of diode laser emitters, we reveal from a physical mechanism perspective that utilizing a transform lens with a shorter focal length can stabilize the modes of edge emitters.