The two-way coupling of WRF and CAM for regional climate modeling requires transferring data (such as wind velocities, temperature, moisture, etc.) between the grids of WRF and CAM. These grids are in general non-matching, and the data transfer should be both physical conservative and numerically accurate. Our method contains two parts: constructing the common refinement and conservative data transfer using the common refinement. The former computes the cell intersections and provides the necessary data structures for the latter. We project the grids of WRF and CAM onto a plain surface using their corresponding map projection methods (such as: Lambert conformal projection). Then common refinement method will locate the edge intersection points of two grids, and determine sub-facets to create a new mesh based on the union of the intersection points and vertices of the original two grids within the overlapping area. After obtaining the common refinement mesh, we use a weighted-residual formulation, which minimizes the L-2 norm of the error, to complete the data transfer. The L-2 minimization method satisfies physical conservation and at the same time is as accurate as interpolation.