The diffusion behavior of methanol in different critical media (n-pentane, n-hexane, n-heptane and acetone) was investigated by the Monte Carlo (MC) method. From the simulation results, the diffusion constant of methanol molecule in the critical n-hexane is much larger than those in n-pentane, n-heptane and acetone. By analyzing the microscopic configurations of the critical mixtures, it is found that the diffusion constant of methanol is related to the local solvent clustering around methanol, but it does not exhibit strong dependence on the size of solvent cluster around methanol. Moreover, the survival time of the solvent cluster plays an important role in determining the diffusion constant.