In this work, the hierarchical equation of motion approach was employed to study the excitation transfer efficiency (ETE) from the Fenna-Matthews-Olson (FMO) complex to the reaction center core complex (RCC). Further, the realistic initial pure state (created by the interaction of femtosecond laser pulse with the isolated FMO complex) was used in the presence of an inhomogeneous protein environment. We observed the same amount of excitation transfer from the FMO to the RCC, in agreement with the experiment using femtosecond absorption spectroscopy. Simulation analysis shows weak intermonomer couplings are strongly affecting the dynamics of ETE, which implies that all the monomers of the FMO complex need to be considered as connected with the RCC pigment for a better estimate of the ETE.