The energy transfer between a subunit of Fenna-Matthews-Olson antenna complex of green sulfur bacteria and its reaction center (sink) was investigated. Through fixing the site energies of bacteriochlorophyll molecules and the coupling strength between the Bacteriochlorophylls(BChls), a Hamiltonian of the Fenna-Matthews-Olson-sink and its reduced models were constructed. Based on the Hamiltonian, the evolutions of the populations of different BChls and the sink states was investigated by a hierarchical equation of motion approach. In order to observe the coherence between different states in the processes of energy transfer, the two-dimensional third-order photon echo spectra of the Fenna-Matthews-Olson and its reduced models in different waiting times were calculated. The results imply that for energy harvesting there are some redundant chromophores in the Fenna-Matthews-Olson complex.