Heat conduction in carbon nanotubes was simulated by nonequilibrium molecular dynamics method with reactive bond order (REBO) potential.Combined with phonon spectrum analysis based on the first principles，thermal effects of three types of point defects such as doping，absorption and vacancy were analyzed.Influences of major factors including ambient temperature，length and radius of carbon nanotube were studied.Thermal conductivities of carbon nanotubes without defects were also calculated for comparison.Simulation results show that a sharp jump in the temperature profile occurs at defect positions.Thermal conductivity of nanotubes decreases significantly due to point defects.The defect type plays a more important role on the thermal conductivity than the length or the radius of carbon nanotubes.The relative influences of three types of defect on the thermal conductivity are in the order of vacancy>doping> adsorption.