Double pass Rapid Scanning Optical Delay Line (RSOD), as an axial scanning method widely which is used in Optical Coherence Tomography (OCT), is one of key technologies in developing OCT. This thesis was deeply analyzed beam transmission and beam distribution in RSOD under the condition of coupling optimization using matlab, thus increased theoretic arguments for RSOD design, elements choice and system adjustment. The two defocus distances Δf=1 μm and Δf=578 μm were got as theoretic coupling optimization, but concerning the practical adjustment, the defocus distance Δf=1 μm was better.So Δf=1 μm was the coupling optimization of RSOD.