The lattice Boltzmann method is used to simulate the thermal field and flow field of nanofluid Raleigh-Benard convection in a rectangular cavity. The heat transfer characteristics of nanofluid are compared under different Raleigh numbers, volume fractions of nanoparticles and particle sizes. The results show that under the same Raleigh number and volume fraction, the convection heat transfer of nanofluid becomes weakened by increasing the particle size. Under the same Raleigh number and particle size, the convection heat transfer of nanofluid becomes strengthened by increasing the volume fraction of nanoparticles.