Understanding the mode’s origin in planar metamaterials is fundamental for related applications in nanophotonics and plasmonics. For complex planar metamaterials, conventional analysis that directly obtains the final charge/current distribution of a mode is usually difficult in helping to understand the mode’s origin. In this paper, we propose a mode evolution method (MEM) with a core analysis tool, i.e., plasmonic evolution maps (PEMs), to describe the mode evolution in several complementary planar metamaterials with designed plasmonic atoms/molecules. The PEMs could not only clearly explain a mode’s origin, but also reveal the role of a structure’s symmetry in the mode formation process. The MEM with PEMs can work as a simple, efficient, and universal approach for the mode analysis in different kinds of planar metamaterials.