Abstract: The optical limiting effect of the graphene films in midinfrared band (3 m~5 m) was studied using nanosecond pulsed laser Zscan method . The Zscan curve obtained from the open aperture experiment showed a single valley structure, but the same structure did not show in the closedaperture Zscan curve. Through the fitting and calculation of the openaperture Zscan curve, the 3order nonlinear absorption coefficients and the optical limiting thresholds of 3 layers graphene were 11.3910-7cm/W, 10.6110-7cm/W, 9.7510-7cm/W, 8.8110-7 cm/W and 3.49 J/cm2, 3.75 J/cm2, 4.11 J/cm2, 4.55 J/cm2 at 3.010 m, 3.522 m, 4.326 m and 4.880 4 m, respectively. The 3order nonlinear absorption coefficients and the optical limiting thresholds of 3 layers, 5 layers and 7 layers graphene in 3.522 m center wavelength were 10.6110-7cm/W, 11.3210-7cm/W, 11.9510-7cm/W and 3.75 J/cm2，3.41 J/cm2，3.32 J/cm2, respectively. The experimental results show the optical limiting effect of graphene is obvious in the midinfrared band based on nonlinear reverse saturable absorption.