A simple photonic approach to generate tunable microwave signal with a Brillouin fiber ring laser in a figure of eight configuration is proposed and experimentally demonstrated. A dual wavelength optical signal with about 20 GHz or 0.16 nm frequency spacing is achieved by removing the odd-order Stokes lines. The power variation of the first order Stokes and third order Stokes is less than ±0.35 dB. The optical signal is heterodyned at the high speed photodetector (PD) to produce a 21.39 GHz microwave signal. The signal-to-noise rate (SNR) of the microwave signal is about 20 dB. The 3 dB linewidth is estimated as 2 MHz. The power variation of microwave signal is less than ±0.75 dB. 3 dB linewidth of microwave signal is also about 2 MHz by beating Brillouin pump and the second order Stokes. Tunable microwave signal under ±0.28 GHz can be obtained by adjusting the wavelength of pump laser. ~20 GHz tunable microwave signal can be achieved by the proposed scheme, and the result can be used to improved microwave signal in future.