Withered grass bacilli were irradiated respectively by nine output spectral lines (454.5-514.5nm) of Ar+ laser with an irradiation dosage of 3×10-2J/cm2. The frequency dependence of Ar+ laser action on withered grass bacilli was obtained. The experimental results showed that along with the increase of Ar+ laser wavelength (from blue light region to green light region), the promoting reproductive action of Ar+ laser on the withered grass bacilli gradually decreases and finally the restraint reproductive action was produced.