The transimission of 780nm Rb Faraday resonance optical filter（Rb-FROF） is measured experimentally and analysed theoretically as a function of the density of atoms and the intensity of magnetic field.The experimental results show that the tuning capability of Rb-FROF by changing the magnetic field is about 100GHz/T

the coefficient of transmission more than 40%

the bandwidth 0. 001nm￣0. 01nm

and the rejection better than 10￣（-4）.