The present inventive concept relates to a copper based conductive paste and its preparation method. The copper based conductive paste comprises a copolymer-copper composite comprising an imidazole-silane copolymer with partially cross-linked structure and a copper powder, a solvent, a binder and an additive. The imidazole-silane copolymer with partially cross-linked structure is introduced into the copper powder whose surface is treated by a hydrochloric acid aqueous solution and a phosphoric acid aqueous solution. The imidazole-silane copolymer is polymerized by using an imidazole monomer represented by following formula 1, a silane monomer represented by following formula 2 and a cross-linking agent. In Formula 1, X represents a hydrogen atom (H) or a methyl group (—CH3), and R1 represents a vinyl group or an allyl group. In Formula 2, Y represents a methoxy group, a 2-methoxy ethoxy group or an acetoxy group, and R2 represents a vinyl group.