Transmission electron microscopy was used to investigate the formation mechanism of SiC bi-nanowires (BNW) with a Y-shaped junction. Different from the previously reported growth mechanisms, our study suggests that when two individual nanowires that are growing through the vapor-liquid-solid mechanism meet with a proper angle, they will merge and form a straight and symmetric BNW with its two side-branches maintaining their original crystallographic orientations and sharing the same crystallographic growth direction, which can be (110), (112) or (113), depending on the meeting angle between the two initial nanowires. According to our observations, a growth model of SiC BNWs with a Y-shaped junction was proposed. The radii and the microstructure of the BNWs are controlled to a certain extent by the meeting angle and the radii of the two SiC single NWs.