Spectral beam combining of a broad area diode laser is a promising technique for high power direct diode laser applications. Grating external cavity spectral beam combination is based on wavelength selection characteristics of the grating and external cavity diode laser technology to achieve the locking of the single emitter spectrum and the combination of all the sub-beam combining elements into one output. The beam quality of the output is equivalent to that of a single beam combining element, and the brightness and power are greatly improved. An experimental study on the coupler free grating external cavity spectral beam combining of two mini-bar stacks was presented. Spectral beam combination of 12 diode laser short array stripes was realized. The characteristics of spectrum, power, and beam quality of the output beam were analyzed. At the pump current of 70 A, the continuous output power of 578 W, spectral bandwidth of 10.26 nm, and electro-optical conversion efficiency of 46.5% were achieved.