Microwave plasma is considered to be more suitable for magnetic nanoparticles' preparation with advantages of moderate power density, high activity and non-electrode. This paper presents a microwave plasma generator that can excite and maintain microwave plasma much more easily than the previous similar structure [1] by changing the inlet of working gas. The emission spectra of microwave plasma in different experimental conditions and positions were measured to analyze the electron excited temperature by characteristic spectrum, and get the rough distribution of plasma temperature. Centered on the microwave plasma generator, a preparation system was established to manufacture Iron nano-particles. And the manufactured Iron nano-particles had been verified to possess magnetism, distribute homogeneously with the average size about 30nm.