The influences of flow parameters on self-diffusion in a vibrated granular bed were studied by simulation and experiment. Employing image processing technology and a particle tracking method, the local displacements and velocities of particles were measured. The selfdiffusion coefficients were determined from the history of particles' diffusive displacements. Discrete element method simulation was performed to calculate the particles' self-diffusive displacements. The simulation results were compared to the experimental tests. The flow behavior of convection rolls in a vibrated bed occurred by the particles' self-diffusion induced by the energy input from vertical external vibration. The velocity fluctuations, granular temperature and self-diffusions were anisotropic with greatest components in the vertical direction. The dependence of the diffusion coefficients on the dimensionless acceleration amplitude, vibration amplitude, vibration frequency, velocity fluctuations, granular temperature, vibration velocity, restitution coefficient and solid fraction are discussed.