Abstract: Using Lennard-Jones pair potential, the thermal conductivity of nitrogen in a cubic pore of 20 nm in length was calculated by equilibrium molecular dynamics (MD) simulation at 300 K and 0.1 MPa. The distributions of velocity component and speed of molecules calculated by the simulation and the Maxwell distribution equation fit very well. The mean free path of the molecules was strictly confined by the wall size of the nanoscale pore. The thermal conductivity of nitrogen in the nanoscale pore was determined by the Green-Kubo method and separately compared with the experimental and theoretic data in the literatures. The simulation result is close to the experimental one and only about one third of the value in the free space under the same conductions.