Optical emission spectroscopy (OES) is used to diagnose the active species emission in the helicon_wave_plasma_enhanced chemical vapor deposition of nanocrystalline silicon. The effects of the experimental parameters on OES intensity of SiH *, Hβ and Hα have been studied. Ｅxperiment r esults indicate that the ma gnetic field confinement makes the reactant molecules dissociate efficiently. Ap propriate hydrogen dilution can increase the density of hydrogen active species, while higher dilution makes the concentration of silicon_contained active spec ies decrease. The density of the active species increases monotonically with in creasing input rf power, and a relatively higher concentration of hydrogen act ive species reaching the substrate surface can be achieved. Experiment results obtained are analyzed based on the dispersive relation and the characteristic o f the helicon wave plasma, which offer the basic data for the understanding of t he process of nanocrstalline silicon deposition and adjusting its experimental p arameters.