This study uses" HIFRL" type in the intermediate energy heavy ion accelerator (Institute of modern physics of Chinese Academy of Sciences provides) 12C6+ ion beam through mutagenesis. Three alfalfa seeds are irradiated by dose of 0Gy, 200Gy, 400Gy, 800Gy and 1200Gy. The germination experiment of alfalfa seed has been done in the laboratory. And in the field, The germination rate , plant height and branch number of planting experiment in the field have been preliminarily observed. The results show that three kinds of alfalfa seeds irradiated at 200Gy not only improve the germination rate, but also enhance the vitality of seeds. The germination rate , plant height and branch number of three different alfalfa irradiated by heavy beam ion have been changed. The germination rate of ZhongLan No. 1 was 41.7% when the seed of alfalfa were irradiated at dose of 200Gy, which was increased 18.4% compared with the control group. The average height of growth of 40 days alfalfa in ZhongLan No. 1 was 6.68cm in the radiation dose of 800Gy, which was increased 1.2cm compared with the control group. The number of branches Tacheng alfalfa was increased the 0.91 (5.16vs 4.25, P <0.001) by irradiated of 400 Gy ; Branch number in BC-04-744 alfalfa was increased 0.53 (4.69 vs 5.22, P <0.05) in the radiation dose 200Gy; The number of branches in ZhongLan No. 1 was increased 0.92 (5.02 vs 5.94, P <0.001) when seeds were irradiated at dose of 800Gy .which has great significance of practical guidance for breeding alfalfa seeds and solving the problem of low breeding capacity of wild grass seed .