The weak interlayer interaction and strong intralayer bonding in two-dimensional (2D) lamellar materials give rise to ultra-low friction properties when the contacted interface between two crystalline is incommensurate, known as structural superlubricity. The origin of friction in a two-dimensional heterojunction is complicated by the interplay among normal forces, edge effects and twist angle (theta). In this article, molecular dynamics (MD) has been adopted to theoretically investigate the friction characteristics in graphene/MoS2 layered heterojunction. The results demonstrate that friction of graphene/MoS2 interface at theta = 0 degrees is approximately 100 times larger than the one at theta = 30 degrees. Unexpectedly, whether graphene slider experiences in-plane vibrational motion perpendic-ular to the sliding path depends on the initial configuration and relative twist angle. To quantitatively understand the origin of friction, the friction contributions from different edge atoms and internal atoms have been inves-tigated. It is found that friction of the edge perpendicular to the sliding direction is much larger than that of the other edges. In addition, frictions from the front and back edges mostly cancel out at twist angles theta = 0 degrees and 30 degrees.