▎ 摘　　要

Under effective-mass approximation, the Kubo formula is used to calculate the minimal conductivity of graphene. It is found that the minimal conductivity depends on the spectral function of quasiparticle. If the distribution of the spectral function is taken to be Lorentz distribution, the minimal conductivity is 4e(2)/pi h. If the distribution of the spectral function satisfies Gaussian distribution, however, the minimal conductivity is 2e(2)/h.