The invention relates to a carbon-nitrogen-oxygen combined treatment process and device. The process comprises previous cleaning, preheating, nitrocarburizing, oxidizing, waste gas treatment and later cleaning, wherein the waste gas treatment comprises the following steps: 1, introducing poisonous gas in a nitriding furnace into an oxidizing furnace for performing detoxifying treatment; 2, introducing gas in the oxidizing furnace into an absorption tower for performing spraying treatment, and achieving emission on standard. The invention also relates to a carbon-nitrogen-oxygen combined treatment device which comprises a preheating furnace, the nitriding furnace, the oxidizing furnace and a waste gas purification treatment device, wherein the nitriding furnace is communicated with the oxidizing furnace through a first fan and a first pipeline; the oxidizing furnace is communicated with the waste gas purification treatment device through a second fan and a second pipeline; gases in the nitriding furnace enter the oxidizing furnace and are purified through the waste gas purification treatment device for emission. The process and the device have the advantages of high waste gas treatment efficiency, stable process, short aging and high yield, the equipment is simple and practical, and reduction, harmlessness and reclamation in the whole technical process are realized.