The lock of double resonance frequency and spatial separation of two lights with frequency difference of 9.2 GHz in a three-mirror ring cavity and Mach-Zehnder (M-Z) interferometer are designed and confirmed. The double resonance for the two lights is accomplished when cavity length is 391.3 mm, and frequency difference is 9.2 GHz. And then, the two beams are spatial separated with unbalanced M-Z interferometer whose two arms optical path difference is 81.5 mm and phase differenceis π/2. The device lays an experimental foundation for the realization of the optical quantum exchange with a coherent atomic medium in an optical cavity.