With the development of optical fiber communication technologies, high quantum efficiency and high speed photodetectors are more and more essential for long-hual high-bit-rate optical communication systems. The quantum efficiency (QE) of novel dual-absorption resonant cavity enhanced photodetector (RCE-PINIP) is calculated theoretically using transfer matrix method (TMM) and the results are simulated. It is revealed that with the gradual increase of dual-absorption layer thickness in the 50～800 nm range, there will emerge several QE peaks for this RCE-PINIP structure model. And the QE peak firstly increases to the highest value (98.6%) when the thickness of two single absorption layers is both 325 nm, and then the peak gradually decreases. When the thickness of two single absorption layers is fixed at 325nm respectively, dependences of QE on the thickness of other single absorption layer are almost the same. So for this RCE-PINIP model structure, after the optimizations on the thickness of both single absorption layer thickness, an optimized structure which can achieve high QE is obtained.