From the point of view statistic physics and the renormalization group method, we studied the rupturing of a 1-D and a 2-D focal body, after the stress accumulation of the stress accumulation element in the combination model was into the nonlinear period. The critical value of the rupturing probability of the focal bodies is 0.2063, 0.1707 respectively. Using the rupturing critical value of the 2-D focal body, we got the critical ratio of the gap energy to the reference energy is 0.1872 for a seismic gap. The value 0.1872 was examined using ten seismic gaps from 1967 to 1980 and the seismic gaps (starting magnitude: M_L=2, 3) from 1982 to 1986 in the eastern part of China. The results are satisfactory.