Abstract: In order to study the effect of microwave irradiation on germination and growth physiological characteristics of seeds that stored for years, the irradiated alfalfa seeds that stored at room temperature for 2 years were used to conduct the germination and pot culture tests, and the germination rate, radicle elongation, growth height, individual nodule, nitrogenase activity, chlorophyll content and chlorophyll fluorescence parameters were measured. On the 15th day of germination, the germination rates of all the treatments are higher than that of the control, which decrease with the elongation of time. On the 11st day of germination, the radicle length of all the treatments is lower than that of the control. Growth height, individual nodule, fresh weight and dry weight for the 40 s irradiation treatment are higher than that of the control. Nitrogenase activity of all the treatments is lower than that of the control (P<0.05). The chlorophyll content reaches its maximum when being irradiated for 10 s, and the variation for F₀ and F_v/F_m of all treatments indicates that the light conversion efficiency of the leaves derived from the irradiated alfalfa seeds that stored for 2 a at room temperature is still relatively stressed.