Recently, single crystalline two-dimensional (2D) carbonitride, C3N has been synthesized. It has demonstrated outstanding physical properties, including ultra-high stiffness and thermal conductivity, implying potential as 2D solid lubricant. In the present study, we investigated the frictional property at the interfaces of homo-and heterojunction composed of C3N, graphene, and BN via performing the high throughput first-principles calcu-lations. The maximum potential energy corrugation and the corrugation along the minimum energy path at the interfaces of graphene/C3N and BN/C3N heterojunctions are the smallest and highest among the four sliding systems, respectively. Correspondingly, the friction force at graphene/C3N interface under low normal load is low, attributed to the smaller interfacial charge transfer. Besides, the friction force at C3N/C3N interface is lower than that at graphene/graphene interface under normal load less than 46 nN, and that at graphene/C3N interface under 8-54 nN normal load. More importantly, we identified an ultra-low and a much lower friction state enabled by pressure-induced friction collapse at graphene/C3N and C3N/C3N interfaces, respectively. We also demonstrated the effectiveness of incommensurate contact in reducing friction at C3N/C3N interface. Our investigation indicates the promising potential of 2D C3N as atomic-thin solid lubricant.