The nitriding of pure iron by conventional plasma and thermal plasma irradiation were contrastively investigated. The compound nitrides layer of ε and γ′phase can be formed by either of conventional plasma nitriding or thermal plasma irradiation. In comparison with traditional nitriding process, thermal plasma irradiation has a much more increased reaction speed and great reduced nitriding time, which proved the feasibility of this technology, and nitriding of morphology shows a “transformation zone” which constructed by γ′-Fe₄ N or Fe₁₆N₂ mixture phase and which was notable influenced by temperature irradiated, this “transformation zone” have high hardness which can provide a tribological applications. The needle like morphology precipitates in the diffusion zone were not observed under thermal plasma irradiation in comparison with conventional plasma nitrided due to rapid cooling after nitriding which was formed a supersaturation nitriding phase with nitrogen 3.0-4.5 at.%.