Objective To investigate the influence of the SiCl4 and N2 mixture ejection parameter by using a slot nozzle on the siliconizing rate during the preparation of 6. 5% Si steel by CVD method. Methods The siliconizing experiment was conducted at different reaction temperatures, volume fractions of SiCl4 gas, and mixture gas flows. The impact of these factors on the siliconizing rate was analyzed by scanning electron microscope, energy spectrum analysis and weightlessness ratio analysis. And the comparison of siliconizing rates under ejection by slot nozzle and uniform atmosphere was conducted. Results The siliconizing rate was significantly improved by the application of slot nozzle. The siliconizing rate continuously increased with increasing temperature. After the temperature reached 1100 ℃, the siliconizing rate tended to saturate and did not show obvious change with further increase of the temperature. And the siliconizing rate increased firstly and then gradually decreased with the increase of SiCl4 concentrations and mixture gas flows, when the concentration of SiCl4 was 15% , the siliconizing rate reached the maximum; when the gas flow rate was 1 L / min, the siliconizing rate reached the peak value. Conclusions There was a great advantage by using slot nozzle to inject reaction gas in the preparation of 6. 5% Si steel with CVD method. Moreover, the siliconizing rate was the highest when the reaction temperature was 1170 ℃ , SiCl4 gas volume fraction was 15% , and gas mixture flow was 1 L / min.