Here, we propose and verify the possibility of using the Raman field as an intermediate process to excite the Brillouin OFC in a free-space oscillator. As far as we know, this is the highest reported power for any Brillouin OFCs, which is four orders of magnitude higher than that of the micro-resonator-based OFC. This free-space approach provides a new path for realizing high-power OFCs in specific wavelengths.