The FDTD method is employed to analyze several types of Coplanar Waveguide (CPW) to slotline (SL) transitions including the effects of the coaxial connectors, air bridges, shielding effects as well as interactions between discontinuities. Superabsorbing boundary conditions, graded mesh and matched source have been implemented in the code for high accuracy and numerical efficiency. Theoretical simulations show excellent agreement with experimental data appeared in the literature.