Two-dimensional (2D) graphitic carbon nitrides (2D GCNs) are a rising class of 2D polymeric materials. Compared with graphene, they have many attractive merits, such as their great semi-conductivity and photo-catalyticity. Despite much progress in studying their various properties, their thermal properties have been given little attention. In this work, thermal conductivities of three kinds of 2D GCNs, heptazine-based g-C3N4 (HEP), triazine-based g-C3N4 (TRI), and 2D polyaniline g-C3N (PANI), were computationally investigated by non-equilibrium molecule dynamics (NEMD) simulations based on both Tersoff and ReaxFF potentials, which offer comprehensive understanding of their thermal properties. It was found that the PANI was predicted to show extrapolated bulk thermal conductivities of 810 W/(m.K) and 461.9 W/(m.K) by the Tersoff and ReaxFF potentials, respectively. The HEP and TRI have much lower bulk thermal conductivities, ranging from 14.1 to 119 W/(m.K). Nevertheless, they are still much higher than those of traditional polymers. The ReaxFF potential also shows that carbon-nitrogen bonds are stiffer than those modeled by the Tersoff potential, resulting in higher phonon harmonicity, and longer phonon mean free paths. (C) 2018 Elsevier Ltd. All rights reserved.