By means of complex variable functions, symmetrical dynamic extension issues of mode III interface crack were researched. The problems considered can be very facilely transformed into Riemann-Hilbert problem by the approaches of self-similar functions, and the general expressions of analytical solutions of the stresses, displacements and dynamic stress intensity factors for the edges of symmetrical mode III interface crack subjected to motive variable loadings Pt4/x4 and Px5/t4 were attained, respectively. After those solutions were utilized by superposition theorem, the solutions of arbitrary complex problems could be acquired.