Spectral beam combining technology based on dichromatic mirror can overcome the limitation of the output power limit of one single-mode fiber laser, which is an effective technical means to obtain laser output with high power and perfect beam quality. Theoretically, the influence of the beam position shift and tilt error on the quality of the combined beam was preliminarily explored. The results show that the beam tilt error has a significant influence on the output characteristics of the combining system. In the experiment, the combining experiment of two narrow linewidth fiber lasers was carried out. Using dichromatic mirrors as the combining element, a high beam quality and common-aperture combining with 2355 W combined output power was achieved, the beam quality factor M² was 1.9, and the efficiency was greater than 99%, which proves that the dichromatic mirror has high efficiency for both the reflection and transmission cases. The experiment result shows that it is possible to achieve a common aperture laser output with higher power and better beam quality by further increasing the number and power of the channel.