The mathematical character of the extinction efficiency (normalized extinction cross section) is analysed and the numerical computation by Matlab language computer simulation is studied. The relationships between the ripple structure of the extinction efficiency and the size parameter x, the peak value of the ripple structure and the amplitude of Mie scattering a_n(x,m), b_n(x,m) are discussed. The relationship between the approximate periodicity of the ripple structure and relative refractive index m is also discussed. The result shows that the relation curve of the extinction efficiency and the size parameter x has ripple structure, which becomes faint as x is large;when the relative index m is real and m≤2, the ripple structure has single periodicity, and positions of the peak values of the ripple structure are corresponding to the positions of peak values of Re[a_n(x,m)]and Re[b_n(x,m)]. When m is complex and ｜Im(m)｜<0.01,the ripple structure also has the same periodicity,however, the oscillation amplitude of the ripple structure becomes weaker. The larger | Im( m) | is , the weaker the oscillation amplitude of the ripple structure is. The computer simulation results of this paper can provide reference for further study of microsphere.