To simulate the Last Glacial Maximum (LGM), an Earth System Model (COSMOS-ASO, http://cosmos.enes.org/ ), an Ocean(MPIOM, GR30L40)-Atmosphere-Vegetation (ECHAM5-JSBACH, T31L19) fully-coupled model, is utilized according to the 21ka experimental design in PMIP3. Two kinds of sensitive experiments are run to test the responses of COSMOS to different initial forcing of the Ocean. The one forced by the Present Ocean features the similar North Atlantic Deep Water (NADW) formation site and a much stronger Atlantic Ocean meridional overturning circulation (AMOC) compared with control run (pre-industrial period, hereafter PI). However, the one initialized by the cold ocean which is derived from the LGM equilibrium of MPI-OM prescribed to the LGM condition of PMIP2, is characterized by a shallower NADW but a AMOC with the similar strength as PI. It is the properties of Antarctic Bottom Water (AABW) that, to some extent, could contribute to the distinct equilibriums. Besides that, Sea Surface Temperature (SST) distribution is much like the reconstruction data (e.g. GLAMAP) although with some uncertainties, as well as the Sea Surface Salinity (SSS). Additionally, two more experiments are run to check out the AMOC’s sensitivity to the depth of Strait of Gibraltar. It is found that the shallower one could account for about 2~3 Sv increase of AMOC in our COSMOS.