Abstract: Si/C/N nanocom posite powders were synthesized by irradiating a mixture of HMDS and NH₃ with a high power CO₂ laser. The influences of HMDS flow rate and NH₃ on the powder composition were studied. The results show that increasing HMDS flow rate can decrease the carbon content, increase the hydrogen content, and keep the silicon and nitrogen content constant. The addition of NH₃ can greatly decrease the carbon content, and increase the nitrogen content. The asformed powders are amorphous and the mean particle size is 10～50 nm. The production rate of the powder is 62～113 g/h.