An efficient adiabatic coupling is presented in this paper for coupling light between rib dielectric waveguide and 2D photonic crystal waveguide (PCW). Using planar wave expand (PWE) method and FDTD method, the linear and nonlinear taper profiles are compared. Following with these, some widths of the entrance of the taper are compared and the best width is given. Simulation result have proved that transmission ratio above 95% can be obtained in a wider frequency range by usin g a cosine taper profile than line taper profile.