A combination corona discharge reactor includes a rectangular or cylindrical electrically insulative housing and a plurality of reactor units arranged in a parallel or series manner in the housing in a rectangular or circular array. Each reactor unit includes a hollow cylindrical electrode and a rod electrode extending along the longitudinal axis of the hollow cylindrical electrode and a DC working voltage 6 kv-500 kv applied to each reactor unit between the respective hollow cylindrical electrode and the respective rod electrode. The combination corona discharge reactor is a modularized structure constructed subject to actual requirements, practical for decomposing waste lubricating oil, insulation oil, milling oil and smokes discharged from a kitchen, smoking room, motor vehicle or machine.