Abstract: This paper puts forward a new methed of surface thermo-chemical treatment, the high speed Carbo-nitriding method. The diffusion depth can be made to 0.3~ 0.4mm within 2 to 5 minutes by this method.The carbo-nitriding samples (20Cr) were analysed by micrography with electroe microscope, which showed that the contents of carbon and nitrogen on the surface reached 0.91% and 0.46% respectively. Therefore, it is a new heat treating process which the advantages of high speed and easy operation.