Thermal conductivities (TCs) of graphyne-n nanotubes (GNT-n) are investigated by reverse non-equilibrium molecular dynamics simulations. Dependences of the generation number n, diameter d, and length L on TCs of GNT-n are derived with scaling relations and explained from the analysis of phonon density of states. Simulation results reveal that with the increase of the generation number n, TC decreases and scales as lambda similar to n(-0.57). The diameter d has a weak impact on TC and a universal scaling law of lambda similar to d(0.03) at d > 5 nm is derived for all GNT-n. With the increase of the length, the scaling relation between TC and L has a crossover. After the crossover, the scaling exponents are 0.16, 0.07, 0.05, 0.04, 0.03 for n = 1-5, respectively, which are much smaller than the scaling exponent of 0.48 for the carbon nanotube (CNT). TC values of GNT-n are estimated to be 92.4, 43.6, 30.4, 27.4, 23.0 W/(m K) for n = 1-5, respectively, at L = 2.6 mu m by extrapolation, which are two orders of magnitude smaller than 2820.6 W/(m K) of the CNT with the same length. This implies the graphyne-n nanotubes may be more promising thermoelectric materials than the CNT. (C) 2015 Elsevier B.V. All rights reserved.