We carried out a systematic study of the complex organic molecules CH_3_OH, C_2_H_5_OH, (CH_3_)_2_O, HCOOCH_3_, HCOOH, CH_3_COOH, H_2_CO, and CS toward 40 GC molecular clouds. Using the LTE approximation, we derived the physical properties of GC molecular clouds and the abundances of the complex molecules.The abundances of complex organic molecules in the GC are compared with those measured in hot cores and hot corinos, in which these complex molecules are also abundant.