This paper introduces the research work on the extension of multilevel fast multipole algorithm (MLFMA) to 3D complex structures including coating object,thin dielectric sheet,composite dielectric and conductor,cavity.The impedance boundary condition is used for scattering from the object coated by thin lossy material.Instead of volume integral equation,surface integral equation is applied in case of thin dielectric sheet through resistive sheet boundary condition.To realize the fast computation of scattering from composite homogeneous dielectric and conductor,the surface integral equation based on equivalence principle is used.Compared with the traditional volume integral equation,the surface integral equation reduces greatly the number of unknowns.To compute conducting cavity with electrically large aperture,an electric field integral equation is applied.Some numerical results are given to demonstrate the validity and accuracy of the present methods.