Abstract: The layer controlled graphene film CaF2 mirrors were prepared by chemical vapor deposition method to study optical limiting mechanism of the graphene devices in 3 m~5 m infrared band, and an allsolidstate infrared optical parametric oscillator was builted based on a periodic polarization crystal MgO∶PPLN. The experiment about scattering of graphene films in the integrating sphere was carried out by using the idler light in 3 m ~5 m wave band. The normalized curve of scattering signal of graphene films and changes of the incident light were measured. It was found that when the idle light energy was more than 1 J/cm2, and the scattering energy signal with the incident light intensity exhibited a fast nonlinear growth trend. In addition, the growth rate of the scattering energy signal was inversely proportional to the incident wavelength of the idle frequency light, which was proportional to the number of layers of graphene. Results show that the optical limiting mechanism of graphene films in 3 m~5 m in the infrared band might be due to the rapidlyvaporized graphene, the formation of micro plasma ionization and the nonlinear scattering.