Radicals produced by the plasma enhanced chemistry vapour deposition technique in SiCl4 plasma are identified by mass spectrometry using our newly proposed straight-line fit method. Since flow rate is one of the most important parameters in depositing thin films, we present the effects of SiCl4 now rate variation on SiCln (n＜3) densities. The experimental results demonstrate that Si and SiCln (n = 1, 2) densities decrease with increasing SiCli now rate. After reaching the minimum values at a now rate of 17 and 13 seem, respectively, Si and SiCln (n=1,2) densities slightly increase with further increase of How rate to 20.5sccm. These results could be interpreted to which the depletion fraction of SiCl4 decreases and the residence time of SiCl4 molecule becomes shorter, with the increasing SiCl4 flow rate. In order to obtain high-quality poly-Si films with high growth rate, it is better to use smaller Row rate of SiCl4 source gas for depositing films.