In this paper, we present the result of large-volume plasma generated in a three-electrode discharge system.The system consists of micro-discharge electrodes, i.e.slit-shaped cathode boundary layer (CBL) which acts as the preionization source, and a third electrode which acts as a collector of electrons.The discharge characteristics of the system were measured under different conditions and pressures in Argon.It is shown that this system is a.possible way to generate large-volume, high-pressure plasma, and the third electrode plays an important role for the generation of plasma in the outer space of the CBL.