This paper focused on the mutagenicity of microwave irradiation with low-power on ,Lactobacillus casei subsp. rhamnosus, 6013 cooled with circulating water of 20℃. In the parallel experiments by adjusting the power and irradiation time, a mutant strain W4-23 with L-lattic acid production of 124.15g/L higher than 80g/L of the parent strain had been obtained. And the properties of W4-23 with highly producing L-attic acid remained stable after cultured for 8 times and stored for two months at 4℃. It was concluded that the mutagencity could be stimulated under the microwave power of 400W and irradiation length of 20min.