An NVT ensemble single-site model molecular dynamics simulation using a leapfrog algorithm with a constraint method for constant temperature has been applied to calculate the self-diffusion coefficients for pure carbon dioxide and the tracer diffusion coefficients for the carbon dioxide + naphthalene system at 308.2 K in the pressure range from 7 to 20 MPa. The simulation results of the self-diffusion and tracer diffusion coefficients are compared with the experimental data. The calculated tracer diffusion coefficients of carbon dioxide for the carbon dioxide + naphthalene system are slightly smaller than the self-diffusion coefficients for pure carbon dioxide at the same pressures near the critical point of carbon dioxide. However, the anomalous decrease of diffusion coefficients observed in the experimental data for mixture systems is not shown in the present simulation results.