The function of Photosystem I (PSI) is catalyzing one of the initial steps in driving oxygenic photosynthesis in cyanobacteria, algae and higher plants. The recent crystallographic model at 3.3 Å resolution represents the most complete plant PSI structure. The Chlamydomonas reinhardtii PSI-LHCI supercomplex structure is not known since it contains a unique structure having additional subunits of light harvesting complex I (LHCI). We have modeled PSI core and LHCI in order to elucidate the structure of PSI-LHCI supercomplexes of C. reinhardtii. Most of the core subunits are homologous to the higher plants except PsaO and now it has been modeled based on threading. All core subunits were located similarly like pea structure however, PsaO, a new subunit is closely located to the PsaH, PsaI and PsaL subunits. The location of PsaO subunit at this position may suggest that it may be involved in state transition mechanism in C. reinhardtii. From our model, it indicates that there are non-covalent strong inter protein-protein relationship, especially from PSI core to LHCI. Our 3D model may give the structural information for better understanding of PSI-LHCI arrangement and its physiological role in C. reinhardtii as well as other algae, where it serves many biotechnological applications.